Power module substrate, power module, and method for manufacturing power module substrate

ABSTRACT

A power module substrate includes: a ceramics substrate having a surface; and a metal plate connected to the surface of the ceramics substrate, composed of aluminum, and including Cu at a joint interface between the ceramics substrate and the metal plate, wherein a Cu concentration at the joint interface is in the range of 0.05 to 5 wt %.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power module substrate, which isemployed in a semiconductor device controlling a large amount of highvoltage electrical current, a power module including the power modulesubstrate, and a method for manufacturing the power module substrate.

This application is based on and claims priority from Japanese PatentApplication No. 2008-149902, filed on Jun. 6, 2008, Japanese PatentApplication No. 2009-065033, filed on Mar. 17, 2009, Japanese PatentApplication No. 2009-075315, filed on Mar. 26, 2009, Japanese PatentApplication No. 2009-086247, filed on Mar. 31, 2009, and Japanese PatentApplication No. 2009-086248, filed on Mar. 31, 2009, the contents ofwhich are incorporated herein by reference.

2. Background Art

Conventionally, in all of semiconductor elements, a power module is usedfor the power supply.

The amount of heat generated by the power module is relatively high.

Consequently, as a substrate on which the power module is mounted, apower module substrate is used in which a metal plate made of Al(aluminum) is joined to a ceramics substrate composed of, for example,AlN (aluminum nitride), Si₃N₄ (silicon nitride), or Al₂O₃ (aluminumoxide), with an Al—Si system brazing filler metal interposedtherebetween.

In addition, the metal plate is formed as a circuit layer, and asemiconductor chip that is a power element is mounted on the metal platewith a solder material interposed therebetween.

In addition, in order to improve the heat radiation efficiency, astructure in which a metal layer is formed by connecting a metal platecomposed of Al or the like with a lower face of a ceramics substrate,and the entire power module substrate is joined to a heat radiationplate with the metal layer interposed therebetween has been proposed.

Conventionally, in order to reliably obtain the joint strength betweenmetal plates which serve as the circuit layer and the metal layer, and aceramics substrate, for example, technique of having the surfaceroughness of the ceramics substrate being less than 0.5 μm has beenknown, as disclosed in Japanese Unexamined Patent Application, FirstPublication No. H3-234045.

However, when the metal plate is joined to the ceramics substrate, evenif the roughness surface of the ceramics substrate is simply reduced,sufficient high joint strength is not obtained and there is adisadvantage in that the reliability thereof cannot be improved.

Even if, for example, a honing treatment is performed on the surface ofthe ceramics substrate by use of Al₂O₃ particles in a dry method and theroughness surface Ra thereof is made 0.2 μm, peeling may occur at aninterface thereof in a peeling test.

In addition, even if a ceramics substrate is polished by use of apolishing method so that the roughness surface Ra is made less than orequal to 0.1 μm, there is a case where peeling occurs at the interfacein the same manner as described above.

In addition, in a case where a power module substrate is subjected to aheat-load cycle, not only peeling at an interface but also cracks beinggenerated in the ceramics substrate is known.

Specifically, recently, in power modules, downsizing and reducing ofthickness has been required, and the usage environment has becomesevere.

The power module is used under a usage environment in which, forexample, heat stress is repeatedly generated.

In addition, recently, the amount of heat generated in an electroniccomponent has tended to increase, so it is necessary to dispose a powermodule substrate on a heat radiation plate as described above.

In this case, since the power module substrate is rigidly fixed to theheat radiation plate, a large shear force is generated at a jointinterface between the metal plate and the ceramics substrate when thesubstrate is subjected to a heat-load cycle.

As a result, improvement of the joint strength and reliability arefurther required.

SUMMARY OF THE INVENTION

The present invention was conceived in view of the above-describedcircumstances and it is an object thereof to provide a power modulesubstrate, a power module including the power module substrate, and amethod for manufacturing the power module substrate, in which a metalplate is reliably connected to a ceramics substrate and the heat-loadcycle reliability thereof is high.

In order to solve the foregoing problem and achieve the object, a powermodule substrate of a first aspect of the present invention includes: aceramics substrate having a surface; and a metal plate connected to thesurface of the ceramics substrate, composed of aluminum, and includingCu at a joint interface between the ceramics substrate and the metalplate, wherein a Cu concentration at the joint interface is in the rangeof 0.05 to 5 wt %.

In the power module substrate having the above-described structure,since Cu is diffused in the metal plate and Cu concentration in thejoint interface is in the range of 0.05 to 5 wt %, the joint interfaceof the metal plate is solid-solution strengthened.

Therefore, when a heat-load cycle or the like is performed, cracks areprevented from being generated and propagated in the metal plate, it ispossible to improve the junction reliability.

In the power module substrate of the first aspect of the presentinvention, it is preferable that an aluminum phase in which Cu isincluded in aluminum, and an eutectic phase composed of a binaryeutectic structure including Al and Cu be formed at an end portion in awidth direction of the metal plate.

In this case, since the eutectic phase composed of a binary eutecticstructure including Al and Cu is formed at the end portion in the widthdirection of the metal plate, it is possible to further strengthen theend portion in the width direction of the metal plate.

Consequently, it is possible to prevent cracks from being generated andpropagated at the end portion in the width direction of the metal plate,and it is possible to improve the junction reliability.

In the power module substrate of the first aspect of the presentinvention, it is preferable that precipitate particles composed of acompound including Cu precipitate in the eutectic phase.

In this case, since the precipitate particles composed of a compoundincluding Cu precipitate in the eutectic phase formed at the end portionin the width direction of the metal plate, it is possible to furtherrealize precipitation strengthening of the end portion in the widthdirection of the metal plate.

Consequently, it is possible to prevent cracks from being generated andpropagated at the end portion in the width direction of the metal plate,and it is possible to reliably improve the junction reliability.

In the power module substrate of the first aspect of the presentinvention, it is preferable that the metal plate include: aconcentration-gradient section in which the Cu concentration graduallydecreases in a manner so as to separate from the joint interface in adirection in which the metal plate and the ceramics substrate arestacked in layers; and a soft layer formed at an opposite side of theceramics substrate relative to the concentration-gradient section,having a degree of hardness lower than that of a near joint interface.

In this case, Cu concentration is high in the metal plate adjacent tothe joint interface, and is hardened due to solid solutionstrengthening.

On the other hand, in the soft layer, Cu concentration is low, thedegree of hardness is low, and the deformation resistance is low.

Therefore, due to the soft layer, it is possible to absorb heat strain(heat stress) which is caused by the difference of the coefficient ofthermal expansion between the metal plate and the ceramics substrate,and it is possible to considerably improve the heat-load cyclereliability.

A power module of a second aspect of the present invention is providedwith: the power module substrate of the above-described first aspect;and an electronic component mounted on the power module substrate.

According to the power module having the above-described structure,since the joint strength between the ceramics substrate and the metalplate is high, even if the power module is used under a severe usageenvironment in which, for example, heat stress is repeatedly generated,it is possible to significantly improve the reliability thereof.

A method for manufacturing a power module substrate of a third aspect ofthe present invention includes: preparing a ceramics substrate, a metalplate composed of aluminum, and a Cu-layer having a thickness of 0.15 μmto 3 μm; stacking the ceramics substrate and the metal plate in layerswith the Cu-layer interposed therebetween (stacking step); pressing theceramics substrate, the Cu-layer, and the metal plate which were stackedin layers in a stacked direction, and heating the ceramics substrate,the Cu-layer, and the metal plate; forming a fusion metal layer at aboundary face between the ceramics substrate and the metal plate(melting step); solidifying the fusion metal layer by cooling the fusionmetal layer (solidifying step); and making Cu to be included into themetal plate adjacent to the joint interface between the ceramicssubstrate and the metal plate in the melting step and the solidifyingstep so that a Cu concentration is in the range of 0.05 to 5 wt %.

In the method for manufacturing a power module substrate, the ceramicssubstrate and the metal plate stacked in layers with the Cu-layerinterposed therebetween, and the ceramics substrate and the metal platewhich were stacked in layers is pressed in the stacked direction andheated.

Because of this, due to the eutectic reaction of Cu of the Cu-layer andAl of the metal plate, the melting point of the near joint interface islowered, even under relatively low-temperature, it is possible to formthe fusion metal layer at the boundary face between the ceramicssubstrate and the metal plate, and it is possible to connect theceramics substrate to the metal plate.

Namely, without using a brazing filler metal composed of Al—Si alloy orthe like, it is possible to connect the ceramics substrate to the metalplate.

As described above, since the ceramics substrate is bonded to the metalplate without using a brazing filler metal, a brazing filler metal doesnot penetrate to a surface of the circuit layer, and it is possible toreliably form a Ni-plated layer on the surface of the circuit layer.

Here, when the thickness of the Cu-layer is less than 0.15 μm, there isa concern that a fusion metal layer cannot be sufficiently formed at theboundary face between the ceramics substrate and the metal plate.

In addition, when the thickness of the Cu-layer exceeds 3 μm, reactantof Cu and Al is excessively generated at the joint interface, the nearjoint interface of the metal plate is strengthened more than necessary,and there is a concern that cracks are generated at the ceramicssubstrate when the ceramics substrate is subjected to a heat-load cycle.

Consequently, it is preferable that the thickness of the Cu-layer be0.15 μm to 3 μm.

In addition, in order to reliably obtain the above-described action andeffect, it is preferable that the thickness of the Cu-layer be 0.5 μm to2.5 μm.

In the method for manufacturing a power module substrate of the thirdaspect of the present invention, it is preferable that the Cu-layer beadhered to at least one of the ceramics substrate and the metal platebefore stacking the ceramics substrate, the Cu-layer, and the metalplate in layers.

In this case, since Cu is adhered to a face of the metal plate(connection face) facing the ceramics substrate or a face of theceramics substrate (connection face) facing the metal plate, it ispossible to stack the ceramics substrate and the metal plate in layerswith the Cu-layer reliably interposed therebetween, and it is possibleto reliably connect the ceramics substrate to the metal plate.

In the method for manufacturing a power module substrate of the thirdaspect of the present invention, it is preferable that, when the Cu isadhered to at least one of the ceramics substrate and the metal plate,Cu be adhered to at least one of the ceramics substrate and the metalplate, by a method selected from an evaporation method, a sputteringmethod, a plating method, and a method of applying a Cu-paste.

In this case, it is possible to form reliably the Cu-layer by a methodselected from the evaporation method, the sputtering method, the platingmethod, and the method of applying a Cu-paste, and it is possible toconnect the ceramics substrate to the metal plate.

In the method for manufacturing a power module substrate of the thirdaspect of the present invention, it is preferable that, when stackingthe ceramics substrate and the metal plate in layers with the Cu-layerinterposed therebetween, the Cu-layer be disposed by inserting a copperfoil between the ceramics substrate and the metal plate.

In this case, due to inserting of Cu-foil, it is possible to form theCu-layer on the face of the metal plate (connection face) facing theceramics substrate or the face of the ceramics substrate (connectionface) facing the metal plate.

Therefore, it is possible to tightly connect the ceramics substrate tothe metal plate.

A power module substrate of a fourth aspect of the present inventionincludes: a ceramics substrate composed of AlN or Si₃N₄, having asurface; a metal plate connected to the surface of the ceramicssubstrate, composed of pure aluminum; and a high-Cu concentrationsection formed at a joint interface between the metal plate and theceramics substrate, having a Cu concentration that is more than twicethe Cu concentration in the metal plate.

In the power module substrate having the above-described structure,since the high-Cu concentration section having a Cu concentration thatis more than twice the Cu concentration in the metal plate is formed atthe joint interface between the ceramics substrate composed of AlN orSi₃N₄ and the metal plate composed of pure aluminum, it is possible toimprove the joint strength between the ceramics substrate and the metalplate due to a Cu atom existing at the near boundary face.

In addition, Cu concentration in the metal plate means a Cuconcentration in the portion that is positioned separately from thejoint interface in the metal plate by a predetermined distance (forexample, 50 nm or more).

In the power module substrate of the fourth aspect of the presentinvention, it is preferable that an oxygen concentration in the high-Cuconcentration section be greater than oxygen concentrations in the metalplate and the ceramics substrate.

In this case, due to oxygen intervening the joint interface, it ispossible to further improve the joint strength between the ceramicssubstrate composed of AlN or Si₃N₄ and the metal plate composed of purealuminum.

In addition, it is thought that the oxygen existing at the jointinterface with a high degree of concentration is oxygen existing at asurface of the ceramics substrate and oxygen taken from an oxide filmformed on a surface of a metal plate.

Here, the oxygen existing at the joint interface with a high degree ofconcentration, this means the oxide film or the like being sufficientlyheated so as to be reliably removed.

Therefore, it is possible to tightly connect the ceramics substrate tothe metal plate.

In the power module substrate of the fourth aspect of the presentinvention, it is preferable that the ceramics substrate be composed ofAlN; and the mass ratio of Al, Cu, O, and N be Al:Cu:O:N=50 to 90 wt %:1to 10 wt %:2 to 20 wt %:25 wt % or less when the joint interfaceincluding the high-Cu concentration section is analyzed by an energydispersive X-ray spectroscopy.

In the power module substrate of the fourth aspect of the presentinvention, it is preferable that the ceramics substrate be composed ofSi₃N₄; and the mass ratio of Al, Si, Cu, O, and N be Al:Si:Cu:O:N=15 to45 wt %:15 to 45 wt %:1 to 10 wt %:2 to 20 wt %:25 wt % or less when thejoint interface including the high-Cu concentration section is analyzedby an energy dispersive X-ray spectroscopy.

When the mass ratio of Cu atom existing at the joint interface exceeds10 wt %, the reactant of Cu and Al is excessively generated, there is aconcern that the reactant interferes the junction.

In addition, the near joint interface of the metal plate is strengthenedmore than necessary due to the reactant, a stress operates in theceramics substrate when the ceramics substrate is subjected to aheat-load cycle, and there is a concern that the ceramics substrate iscracked.

On the other hand, when the mass ratio of Cu atom is less than 1 wt %,there is a concern that it is impossible to sufficiently improve thejoint strength due to a Cu atom.

Therefore, it is preferable that the mass ratio of Cu atom be in therange of 1 to 10 wt % at the joint interface.

In addition, when the mass ratio of oxygen atom including the high-Cuconcentration section and existing at the joint interface exceeds 20 wt%, the thickness of portion in which the oxygen concentration is highincreases, and cracks are generated at the high-concentration sectionwhen a heat-load cycle is performed.

Because of this, there is a concern that, junction reliability isdegraded.

Therefore, it is preferable that the oxygen concentration be 2 to 20 wt%.

Here, when analyzation is performed by an energy dispersive X-rayspectroscopy, since the diameter of the spot therefor is extremelysmall, a plurality of points are measured on the joint interface (forexample, 10 to 100 points), and the average of the points is calculated.

In addition, when the measuring is performed, the joint interfacebetween the crystalline grain and the ceramics substrate is onlymeasured, and the joint interface between the crystalline grain boundaryof the metal plate and the ceramics substrate is not measured.

In addition, in this specification, analytical values are obtained byuse of an energy dispersive X-ray spectroscopy under the condition wherean acceleration voltage is set to 200 kV by use of an energy-dispersiveX-ray fluorescence spectrometer, NORAN System 7 produced by ThermoFisher Scientific Inc., the spectrometer being mounted on an electronmicroscope, JEM-2010F produced by JEOL Ltd.

A power module of a fifth aspect of the present invention is providedwith: the power module substrate of the above-described fourth aspect;and an electronic component mounted on the power module substrate.

According to the power module having the above-described structure, thejoint strength between the ceramics substrate and the metal plate ishigh, and even if the power module is used under a severe usageenvironment in which, for example, heat stress is repeatedly generated,it is possible to significantly improve the reliability thereof.

A method for manufacturing a power module substrate of a sixth aspect ofthe present invention includes: preparing a ceramics substrate composedof AlN, a metal plate composed of pure aluminum, and a Cu-layer having athickness of 0.15 μm to 3 μm; stacking the ceramics substrate and themetal plate in layers with the Cu-layer interposed therebetween(stacking step); pressing the ceramics substrate, the Cu-layer, and themetal plate which were stacked in layers in a stacked direction, andheating the ceramics substrate, the Cu-layer, and the metal plate;forming a fusion aluminum layer at a boundary face between the ceramicssubstrate and the metal plate (melting step); solidifying the fusionaluminum layer by cooling the fusion aluminum layer (solidifying step);and forming a high-Cu concentration section at a joint interface betweenthe ceramics substrate and the metal plate in the melting step and thesolidifying step, the high-Cu concentration section having a Cuconcentration that is more than twice the Cu concentration in the metalplate.

In the method for manufacturing a power module substrate, the ceramicssubstrate and the metal plate stacked in layers with the Cu-layerinterposed therebetween, and the ceramics substrate and the metal platewhich were stacked in layers is pressed in the stacked direction andheated.

Because of this, due to the eutectic reaction of Cu of the Cu-layer andAl of the metal plate, the melting point of the near joint interface islowered, even under relatively low-temperature, it is possible to formthe fusion aluminum layer at the boundary face between the ceramicssubstrate and the metal plate, and it is possible to connect theceramics substrate to the metal plate.

Namely, without using a brazing filler metal composed of Al—Si alloy orthe like, it is possible to connect the ceramics substrate to the metalplate.

In addition, when the thickness of the Cu-layer is less than 0.15 μm,there is a concern that a fusion aluminum layer cannot be sufficientlyformed at the boundary face between the ceramics substrate and the metalplate.

In addition, when the thickness of the Cu-layer exceeds 3 μm, reactantof Cu and Al is excessively generated at the joint interface, the nearjoint interface of the metal plate is strengthened more than necessary,and there is a concern that cracks are generated at the ceramicssubstrate composed of AlN when the ceramics substrate is subjected to aheat-load cycle.

Consequently, in a case where the ceramics substrate is composed of AlN,it is preferable that the thickness of the Cu-layer be 0.15 μm to 3 μm.

A method for manufacturing a power module substrate of a seventh aspectof the present invention includes: preparing a ceramics substratecomposed of Si₃N₄, a metal plate composed of pure aluminum, and aCu-layer having a thickness of 0.15 μm to 3 μm; stacking the ceramicssubstrate and the metal plate in layers with the Cu-layer interposedtherebetween (stacking step); pressing the ceramics substrate, theCu-layer, and the metal plate which were stacked in layers in a stackeddirection, and heating the ceramics substrate, the Cu-layer, and themetal plate; forming a fusion aluminum layer at a boundary face betweenthe ceramics substrate and the metal plate (melting step); solidifyingthe fusion aluminum layer by cooling the fusion aluminum layer(solidifying step); and forming a high-Cu concentration section at ajoint interface between the ceramics substrate and the metal plate inthe melting step and the solidifying step, the high-Cu concentrationsection having a Cu concentration that is more than twice the Cuconcentration in the metal plate.

In the method for manufacturing a power module substrate, the ceramicssubstrate and the metal plate stacked in layers with the Cu-layerinterposed therebetween, and the ceramics substrate and the metal platewhich were stacked in layers is pressed in the stacked direction andheated.

Because of this, due to the eutectic reaction of Cu of the Cu-layer andAl of the metal plate, the melting point of the near joint interface islowered, even under relatively low-temperature, it is possible to formthe fusion aluminum layer at the boundary face between the ceramicssubstrate and the metal plate, and it is possible to connect theceramics substrate to the metal plate.

Namely, without using a brazing filler metal composed of Al—Si alloy orthe like, it is possible to connect the ceramics substrate to the metalplate.

In addition, when the thickness of the Cu-layer is less than 0.15 μm,there is a concern that a fusion aluminum layer cannot be sufficientlyformed at the boundary face between the ceramics substrate and the metalplate.

In addition, when the thickness of the Cu-layer exceeds 3 μm, thereactant of Cu and Al is excessively generated at the joint interface,there is a concern that the reactant interferes the junction.

Consequently, in a case where the ceramics substrate is composed ofSi₃N₄, it is preferable that the thickness of the Cu-layer be 0.15 μm to3 μm.

In the method for manufacturing a power module substrate of the sixthaspect or the seventh aspect of the present invention, it is preferablethat, when stacking the ceramics substrate and the metal plate in layerswith the Cu-layer interposed therebetween, the Cu-layer be disposed byinserting a copper foil between the ceramics substrate and the metalplate.

In the method for manufacturing a power module substrate of the sixthaspect or the seventh aspect of the present invention, it is preferablethat the Cu-layer be adhered to at least one of the ceramics substrateand the metal plate before stacking the ceramics substrate, theCu-layer, and the metal plate in layers.

In the method for manufacturing a power module substrate of the sixthaspect or the seventh aspect of the present invention, it is preferablethat, when the Cu is adhered to at least one of the ceramics substrateand the metal plate, Cu be adhered to at least one of the ceramicssubstrate and the metal plate, by a method selected from an evaporationmethod, a sputtering method, a plating method, and a method of applyinga Cu-paste.

According to the methods, between the ceramics substrate and the metalplate, it is possible to form a Cu-layer having a desired thickness, andit is possible to reliably connect the ceramics substrate to the metalplate.

A power module substrate of an eighth aspect of the present inventionincludes: a ceramics substrate composed of Al₂O₃, having a surface; ametal plate connected to the surface of the ceramics substrate, composedof pure aluminum; and a high-Cu concentration section formed at a jointinterface between the metal plate and the ceramics substrate, having aCu concentration that is more than twice the Cu concentration in themetal plate.

In the power module substrate having the above-described structure,since the high-Cu concentration section having a Cu concentration thatis more than twice the Cu concentration in the metal plate is formed atthe joint interface between the ceramics substrate composed of Al₂O₃ andthe metal plate composed of pure aluminum, it is possible to improve thejoint strength between the ceramics substrate and the metal plate due toa Cu atom existing at the near boundary face.

In addition, Cu concentration in the metal plate means a Cuconcentration in the portion that is positioned separately from thejoint interface in the metal plate by a predetermined distance (forexample, 50 nm or more).

In the power module substrate of the eighth aspect of the presentinvention, it is preferable that the mass ratio of Al, Cu, and O beAl:Cu:O=50 to 90 wt %:1 to 10 wt %:0 to 45 wt % when the joint interfaceincluding the high-Cu concentration section is analyzed by an energydispersive X-ray spectroscopy.

When the mass ratio of Cu atom existing at the joint interface exceeds10 wt %, the reactant of Cu and Al is excessively generated, there is aconcern that the reactant interferes the junction.

On the other hand, when the mass ratio of Cu atom is less than 1 wt %,there is a concern that it is impossible to sufficiently improve thejoint strength due to a Cu atom.

Therefore, it is preferable that the mass ratio of Cu atom be in therange of 1 to 10 wt % at the joint interface.

Here, when analyzation is performed by an energy dispersive X-rayspectroscopy, since the diameter of the spot therefor is extremelysmall, a plurality of points are measured on the joint interface (forexample, 10 to 100 points), and the average of the points is calculated.

In addition, when the measuring is performed, the joint interfacebetween the crystalline grain and the ceramics substrate is onlymeasured, and the joint interface between the crystalline grain boundaryof the metal plate and the ceramics substrate is not measured.

A power module of a ninth aspect of the present invention is providedwith: the power module substrate of the above-described eighth aspect;and an electronic component mounted on the power module substrate.

According to the power module having the above-described structure, thejoint strength between the ceramics substrate and the metal plate ishigh, and even if the power module is used under a severe usageenvironment in which, for example, heat stress is repeatedly generated,it is possible to significantly improve the reliability thereof.

A method for manufacturing a power module substrate of a tenth aspect ofthe present invention includes: preparing a ceramics substrate composedof Al₂O₃, a metal plate composed of pure aluminum, and a Cu-layer havinga thickness of 0.15 μm to 3 μm; stacking the ceramics substrate and themetal plate in layers with the Cu-layer interposed therebetween(stacking step); pressing the ceramics substrate, the Cu-layer, and themetal plate which were stacked in layers in a stacked direction, andheating the ceramics substrate, the Cu-layer, and the metal plate;forming a fusion aluminum layer at a boundary face between the ceramicssubstrate and the metal plate (melting step); solidifying the fusionaluminum layer by cooling the fusion aluminum layer (solidifying step);and forming a high-Cu concentration section at a joint interface betweenthe ceramics substrate and the metal plate in the melting step and thesolidifying step, the high-Cu concentration section having a Cuconcentration that is more than twice the Cu concentration in the metalplate.

In the method for manufacturing a power module substrate, the ceramicssubstrate and the metal plate stacked in layers with the Cu-layerinterposed therebetween, and the ceramics substrate and the metal platewhich were stacked in layers is pressed in the stacked direction andheated.

Because of this, due to the eutectic reaction of Cu of the Cu-layer andAl of the metal plate, the melting point of the near joint interface islowered, even under relatively low-temperature, it is possible to formthe fusion aluminum layer at the boundary face between the ceramicssubstrate and the metal plate, and it is possible to connect theceramics substrate to the metal plate.

Namely, without using a brazing filler metal composed of Al—Si alloy orthe like, it is possible to connect the ceramics substrate to the metalplate.

In addition, when the thickness of the Cu-layer is less than 0.15 μm,there is a concern that a fusion aluminum layer cannot be sufficientlyformed at the boundary face between the ceramics substrate and the metalplate.

In addition, when the thickness of the Cu-layer exceeds 3 μm, reactantof Cu and Al is excessively generated at the joint interface, the nearjoint interface of the metal plate is strengthened more than necessary,and there is a concern that cracks are generated at the ceramicssubstrate composed of Al₂O₃ when the ceramics substrate is subjected toa heat-load cycle.

Consequently, in a case where the ceramics substrate is composed ofAl₂O₃, it is preferable that the thickness of the Cu-layer be 0.15 μm to3 μm.

In the method for manufacturing a power module substrate of the tenthaspect of the present invention, it is preferable that, when stackingthe ceramics substrate and the metal plate in layers with the Cu-layerinterposed therebetween, the Cu-layer be disposed by inserting a copperfoil between the ceramics substrate and the metal plate.

In the method for manufacturing a power module substrate of the tenthaspect of the present invention, it is preferable that the Cu-layer beadhered to at least one of the ceramics substrate and the metal platebefore stacking the ceramics substrate, the Cu-layer, and the metalplate in layers.

In the method for manufacturing a power module substrate of the tenthaspect of the present invention, it is preferable that, when the Cu isadhered to at least one of the ceramics substrate and the metal plate,Cu be adhered to at least one of the ceramics substrate and the metalplate, by a method selected from an evaporation method, a sputteringmethod, a plating method, and a method of applying a Cu-paste.

According to the methods, between the ceramics substrate and the metalplate, it is possible to form a Cu-layer having a desired thickness, andit is possible to reliably connect the ceramics substrate to the metalplate.

A power module substrate of an eleventh aspect of the present inventionincludes: a ceramics substrate having a surface; a metal plate connectedto the surface of the ceramics substrate via a brazing filler metalincluding Si, composed of aluminum; Cu introduced into the jointinterface between the ceramics substrate and the metal plate, whereinthe metal plate includes Si and Cu; and a Si concentration is in therange of 0.05 to 0.5 wt % and a Cu concentration is in the range of 0.05to 1.0 wt %, in a portion which is close to the joint interface of themetal plate.

In the power module substrate having the above-described structure, theceramics substrate is bonded to the metal plate composed of aluminum byuse of the brazing filler metal including Si, and Cu is introduced intothe joint interface between the metal plate and the ceramics substrate.

Here, since Cu is chemical element having the reactivity that is greaterthan that of Al, due to Cu existing at the joint interface, a surface ofthe metal plate composed of aluminum is activated.

Therefore, even if the connecting is performed under the junctioncondition where a temperature is relatively low in a short time by useof a commonly-used Al—Si system brazing filler metal, it is possible totightly connect the ceramics substrate to the metal plate.

In addition, in a method for introducing Cu into the joint interface, Cumay be adhered to a surface of the ceramics substrate and the brazingfiller metal by an evaporation method, a sputtering method, a platingmethod, or the like, or Cu may be included in a Al—Si system brazingfiller metal.

In addition, since Cu is diffused in the metal plate and the Cuconcentration in the portion which is close to the joint interface is inthe range of 0.05 to 1.0 wt %, the portion which is close to the jointinterface of the metal plate is solid-solution strengthened.

Consequently, it is possible to prevent fractures from being generatedin the metal plate part, and it is possible to improve the junctionreliability.

Furthermore, the ceramics substrate is bonded to the metal platecomposed of aluminum by use of the brazing filler metal including Si, Siis diffused in the metal plate, the Si concentration in portion which isclose to the joint interface is in the range of 0.05 to 0.5 wt %.

For this reason, the brazing filler metal is reliably molten and in asolid-solution state, Si is sufficiently diffused in the metal plate,and the ceramics substrate is tightly connected to the metal plate.

In the power module substrate of the eleventh aspect of the presentinvention, it is preferable that a width of the ceramics substrate begreater than a width of the metal plate; an aluminum phase in which Siand Cu are included in aluminum, a Si phase in which a content rate ofSi is greater than or equal to 98 wt %, and an eutectic phase composedof a ternary eutectic structure including Al, Cu, and Si be formed at anend portion in a width direction of the metal plate.

In this case, since not only the aluminum phase in which Si and Cu arediffused in aluminum but also the Si phase in which the content rate ofSi is greater than or equal to 98 wt %, and the eutectic phase composedof the ternary eutectic structure including Al, Cu, and Si are formed atthe end portion in the width direction of the metal plate, it ispossible to strengthen the end portion in the width direction of themetal plate.

In the power module substrate of the eleventh aspect of the presentinvention, it is preferable that precipitate particles composed of acompound including Cu precipitate in the eutectic phase.

In this case, in the eutectic phase formed at the end portion in thewidth direction of the metal plate, since the precipitate particlescomposed of a compound including Cu precipitate, it is possible tofurther realize precipitation strengthening of the end portion in thewidth direction of the metal plate.

Consequently, it is possible to prevent fractures from being generatedat the end portion in the width direction of the metal plate, and it ispossible to improve the junction reliability.

The power module substrate of the eleventh aspect of the presentinvention may include a high-Si concentration section formed at thejoint interface between the metal plate and the ceramics substrate,having a Si concentration that is more than five times the Siconcentration in the metal plate, and the ceramics substrate may becomposed of AlN or Al₂O₃.

In this case, since the high-Si concentration section having the Siconcentration that is more than five times the Si concentration in themetal plate is formed at the joint interface between the metal plate andthe ceramics substrate, due to a Si atom existing the joint interface,the joint strength between the ceramics substrate composed of AlN orAl₂O₃ and the metal plate composed of aluminum is improved.

In addition, here, Si concentration in the metal plate means a Siconcentration in the portion that is positioned separately from thejoint interface in the metal plate by a predetermined distance (forexample, 50 nm or more).

it is thought that the Si existing at the joint interface with a highdegree of concentration is Si mainly included in a brazing filler metal.

When the connecting is performed, Si is diffused in aluminum (metalplate), the amount thereof decreases at the joint interface, a boundaryface portion between the ceramics and aluminum (metal plate) becomes asite of nonuniform nucleation, Si atoms remain at the boundary faceportion, and the high-Si concentration section having the Siconcentration that is more than five times the Si concentration in themetal plate is formed.

The power module substrate of the eleventh aspect of the presentinvention may include a high-oxygen concentration section formed at thejoint interface between the metal plate and the ceramics substrate,having an oxygen concentration that is greater than oxygenconcentrations in the metal plate and in the ceramics substrate, andhaving a thickness of less than or equal to 4 nm, and the ceramicssubstrate may be composed of AlN or Si₃N₄.

In this case, since the high-oxygen concentration section having theoxygen concentration that is greater than the oxygen concentrations inthe metal plate and in the ceramics substrate at the joint interfacebetween the ceramics substrate composed of AlN or Si₃N₄ and the metalplate composed of aluminum, the joint strength between the ceramicssubstrate composed of AlN or Si₃N₄ and the metal plate composed ofaluminum is improved due to the oxygen existing at the joint interface.

Moreover, since the thickness of the high-oxygen concentration sectionis less than or equal to 4 nm, generation of crack is suppressed in thehigh-oxygen concentration section due to the stress when a heat-loadcycle is performed.

In addition, here, oxygen concentrations in the metal plate and in theceramics substrate means an oxygen concentration in the portion that ispositioned separately from the joint interface in the metal plate and inthe ceramics substrate by a predetermined distance (for example, 50 nmor more).

In addition, it is thought that the oxygen existing at the jointinterface with a high degree of concentration is oxygen existing at asurface of the ceramics substrate and oxygen taken from an oxide filmformed on a surface of a brazing filler metal.

Here, the oxygen existing at the joint interface with a high degree ofconcentration, this means that the oxide film or the like issufficiently heated so as to be reliably removed.

Therefore, it is possible to tightly connect the ceramics substrate tothe metal plate.

A power module of a twelfth aspect of the present invention is providedwith: the power module substrate of the above-described eleventh aspect;and an electronic component mounted on the power module substrate.

According to the power module having the above-described structure, thejoint strength between the ceramics substrate and the metal plate ishigh, and even if the power module is used under a severe usageenvironment in which, for example, heat stress is repeatedly generated,it is possible to significantly improve the reliability thereof.

A method for manufacturing a power module substrate of a thirteenthaspect of the present invention includes: preparing a ceramics substratehaving a connection face, a metal plate composed of aluminum, and abrazing filler metal including Si; stacking the ceramics substrate andthe metal plate in layers with the brazing filler metal interposedtherebetween (stacking step); heating the ceramics substrate, thebrazing filler metal, and the metal plate which are stacked in layers ina state where a pressure is applied thereon; forming a fusion aluminumlayer at a boundary face between the ceramics substrate and the metalplate by melting the brazing filler metal (melting step); andsolidifying the fusion aluminum layer (solidifying step), wherein Cu isadhered to at least one of the connection face of the ceramics substrateand a face of the brazing filler metal opposing the ceramics substratebefore stacking the ceramics substrate and the metal plate in layerswith the brazing filler metal interposed therebetween (adhering step).

The method for manufacturing a power module substrate has a Cu-adheringstep in which Cu is adhered to at least one of the connection face ofthe ceramics substrate and a face of the brazing filler metal opposingthe ceramics substrate, before performing the stacking step in which theceramics substrate and the metal plate are stacked in layers with thebrazing filler metal including Si interposed therebetween.

Consequently, Cu is reliably introduced into the joint interface betweenthe ceramics substrate and the metal plate, the surface of the metalplate is activated due to Cu, even if the ceramics substrate is bondedto the metal plate under the junction condition where a temperature isrelatively low in a short time by use of a commonly-used Al—Si systembrazing filler metal, it is possible to tightly connect the ceramicssubstrate to the metal plate.

In the method for manufacturing a power module substrate of thethirteenth aspect of the present invention, it is preferable that Cu beadhered to at least one of the connection face of the ceramics substrateand a face of the brazing filler metal opposing the ceramics substrateby an evaporation method or a sputtering method in the adhering of Cu.

In this case, Cu is reliably adhered to at least one of the connectionface of the ceramics substrate and the face of the brazing filler metalby the evaporation method or the sputtering method, and Cu can reliablyexist at the joint interface between the ceramics substrate and themetal plate.

For this reason, the surface of the metal plate is activated due to Cu,and it is possible to tightly connect the ceramics substrate to themetal plate.

EFFECTS OF THE PRESENT INVENTION

According to the present invention, it is possible to provide a powermodule substrate in which a metal plate is reliably connected to aceramics substrate and heat-load cycle reliability is high, a powermodule which is provided with the power module substrate, and a methodfor manufacturing the power module substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a power module inwhich a power module substrate of a first embodiment of the presentinvention is employed.

FIG. 2 is an explanatory diagram showing a Cu concentration distributionin a circuit layer and a metal layer of the power module substrate ofthe first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an end portion in a widthdirection of the circuit layer and the metal layer (metal plate) of thepower module substrate of the first embodiment of the present invention.

FIGS. 4A to 4C are cross-sectional views showing a method formanufacturing a power module substrate of the first embodiment of thepresent invention.

FIGS. 5A to 5C are cross-sectional views showing a near joint interfacebetween the metal plate and the ceramics substrate in FIGS. 4A to 4C.

FIG. 6 is a diagram showing an evaluation result of junction reliabilityin a first example.

FIG. 7 is a diagram showing an evaluation result of junction reliabilityin the first example.

FIG. 8 is a schematic cross-sectional view showing a power module inwhich a power module substrate of a second embodiment of the presentinvention is employed.

FIG. 9 is a schematic cross-sectional view showing the joint interfacebetween a circuit layer, a metal layer (metal plate), and a ceramicssubstrate of the power module substrate of the second embodiment of thepresent invention.

FIGS. 10A to 10C are cross-sectional views showing a method formanufacturing a power module substrate of the second embodiment of thepresent invention.

FIGS. 11A to 11C are cross-sectional views showing a near jointinterface between the metal plate and the ceramics substrate in FIGS.10A to 10C.

FIG. 12 is a schematic cross-sectional view showing a power module inwhich a power module substrate of a third embodiment of the presentinvention is employed.

FIG. 13 is a schematic cross-sectional view showing the joint interfacebetween a circuit layer, a metal layer (metal plate), and a ceramicssubstrate of the power module substrate of the third embodiment of thepresent invention.

FIGS. 14A to 14D are cross-sectional views showing a method formanufacturing a power module substrate of the third embodiment of thepresent invention.

FIGS. 15A to 15C are cross-sectional views showing a near jointinterface between the metal plate and the ceramics substrate in FIGS.14A to 14D.

FIGS. 16A and 16B are diagrams showing an evaluation result of crackingin a ceramics substrate in a second example.

FIGS. 17A and 17B are diagrams showing an evaluation result of junctionreliability in the second example.

FIGS. 18A and 18B are diagrams showing an evaluation result of crackingin a ceramics substrate in a third example.

FIGS. 19A and 19B are diagrams showing an evaluation result of junctionreliability in the third example.

FIG. 20 is a schematic cross-sectional view showing a power module inwhich a power module substrate of a fourth embodiment of the presentinvention is employed.

FIG. 21 is a schematic cross-sectional view showing the joint interfacebetween a circuit layer, a metal layer (metal plate), and a ceramicssubstrate of the power module substrate of the fourth embodiment of thepresent invention.

FIGS. 22A to 22C are cross-sectional views showing a method formanufacturing a power module substrate of the fourth embodiment of thepresent invention.

FIGS. 23A to 23C are cross-sectional views showing a near jointinterface between the metal plate and the ceramics substrate in FIGS.22A to 22C.

FIGS. 24A and 24B are diagrams showing an evaluation result of crackingin a ceramics substrate in a fourth example.

FIGS. 25A and 25B are diagrams showing an evaluation result of junctionreliability in the fourth example.

FIG. 26 is a schematic cross-sectional view showing a power module inwhich a power module substrate of a fifth embodiment of the presentinvention is employed.

FIG. 27 is an explanatory diagram showing a Si concentrationdistribution and a Cu concentration distribution in a circuit layer anda metal layer of the power module substrate of the fifth embodiment ofthe present invention.

FIG. 28 is an explanatory diagram showing an end portion in a widthdirection of the joint interface between the circuit layer, the metallayer (metal plate), and the ceramics substrate of the power modulesubstrate of the fifth embodiment of the present invention.

FIG. 29 is a schematic cross-sectional view showing the joint interfacebetween a circuit layer, a metal layer (metal plate), and a ceramicssubstrate of the power module substrate of the fifth embodiment of thepresent invention.

FIGS. 30A to 30C are cross-sectional views showing a method formanufacturing a power module substrate of the fifth embodiment of thepresent invention.

FIGS. 31A to 31C are cross-sectional views showing a near jointinterface between the metal plate and the ceramics substrate in FIG. 29.

FIG. 32 is a schematic cross-sectional view showing a power module inwhich a power module substrate of a sixth embodiment of the presentinvention is employed.

FIG. 33 is a schematic cross-sectional view showing the joint interfacebetween a circuit layer, a metal layer (metal plate), and a ceramicssubstrate of the power module substrate of the sixth embodiment of thepresent invention.

FIG. 34 is a cross-sectional view showing a power module substrate usedfor a comparison experiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to attached drawings.

First Embodiment

FIG. 1 shows a power module substrate and a power module of a firstembodiment of the present invention.

The power module 1 includes a power module substrate 10 on which acircuit layer 12 is disposed, a semiconductor chip 3 which is bonded toa top face of the circuit layer 12 with a solder layer 2 interposedtherebetween, and a heatsink 4.

Here, the solder layer 2 is a solder material, for example, a Sn—Agsystem, a Sn—In system, or a Sn—Ag—Cu system.

In addition, in the first embodiment, a Ni plated layer (not shown inthe figure) is provided between the circuit layer 12 and the solderlayer 2.

The power module substrate 10 includes a ceramics substrate 11, thecircuit layer 12 that is disposed on a first face of the ceramicssubstrate 11 (upper face in FIG. 1) and a metal layer 13 that isdisposed on a second face of the ceramics substrate 11 (lower face inFIG. 1).

The ceramics substrate 11 is a substrate used for preventing anelectrical connection between the circuit layer 12 and the metal layer13, and is made of AlN (aluminum nitride) with a high level ofinsulation.

In addition, the thickness of the ceramics substrate 11 is in a range of0.2 to 1.5 mm, and is 0.635 mm in the first embodiment.

In addition, as shown in FIG. 1, the width of the ceramics substrate 11is greater than the widths of the circuit layer 12 and the metal layer13 in the first embodiment.

By connecting a metal plate 22 having a conductive property to the firstface of the ceramics substrate 11, the circuit layer 12 is formed.

In the first embodiment, by connecting the metal plate 22 constituted ofa rolled plate composed of aluminum having a purity of 99.99% or more (aso-called 4N aluminum) to the ceramics substrate 11, the circuit layer12 is formed thereon.

By connecting a metal plate 23 to the second face of the ceramicssubstrate 11, the metal layer 13 is formed.

In the first embodiment, due to connecting the metal plate 23constituted of a rolled plate composed of aluminum having a purity of99.99% or more (a so-called 4N aluminum) to the ceramics substrate 11,the metal layer 13 is formed in a manner similar to the circuit layer12.

The heatsink 4 is a component for cooling the above-described powermodule substrate 10, and provided with a top panel section 5 connectedto the power module substrate 10, and a flow passage 6 through which acooling medium (for example, cooling water) flows.

The heatsink 4 (top panel section 5) is desirably composed of a materialhaving excellent thermal conductivity, composed of A6063 (aluminumalloy) in the first embodiment.

In addition, in the first embodiment, a buffer layer 15 composed ofaluminum, an aluminum alloy, or a combination of materials includingaluminum (for example, AlSiC or the like) is provided between the toppanel section 5 of the heatsink 4 and the metal layer 13.

Consequently, as shown in FIGS. 1 and 2, in the center portion in thewidth direction of the joint interface 30 between the ceramics substrate11 and the circuit layer 12 (metal plate 22), and in the center portion(portion A in FIG. 1) in the width direction of the joint interface 30between the ceramics substrate 11 and the metal layer 13 (metal plate23), Cu is diffused in the circuit layer 12 (metal plate 22) and in themetal layer 13 (metal plate 23), and a concentration-gradient layer 33(concentration-gradient section) is formed in which the Cu concentrationgradually decreases with increases in the distance from the jointinterface 30 in a stacked direction.

In addition, in this specification, “stacked direction” represents thedirection in which the ceramics substrate 11, the circuit layer 12, andthe metal layer 13 are stacked in layers.

Here, the Cu concentration in the portion which is close to the jointinterface 30 of the concentration-gradient layer 33 is in the range of0.05 to 5 wt %.

In addition, the Cu concentration in the portion which is close to thejoint interface 30 of the concentration-gradient layer 33 is the averagevalue of five points which are measured in the range from the jointinterface 30 to 50 μm by use of an EPMA analyzation (diameter of spot is30 μm).

In addition, a soft layer 34 which has a Cu concentration lower than theCu concentration in the near joint interface 30 and has a low degree ofhardness is formed at the opposite side of the ceramics substrate 11 inthe concentration-gradient layer 33 (lower side in FIG. 2).

In addition, in the end portion in the width direction of the jointinterface 30 between the ceramics substrate 11 and the circuit layer 12(metal plate 22), and in the end portion (portion B in FIG. 1) in thewidth direction of the joint interface 30 between the ceramics substrate11 and the metal layer 13 (metal plate 23), as shown in FIG. 3, analuminum phase 41 in which Cu is diffused in aluminum in asolid-solution state, and an eutectic phase 42 composed of a binaryeutectic structure including Al and Cu are formed.

In addition, precipitate particles composed of a compound including Cu(for example, CuAl₂) precipitate in the eutectic phase 42.

The foregoing power module substrate 10 is manufactured as describedbelow.

At first, as shown in FIGS. 4A and 5A, a ceramics substrate 11 composedof AlN, a metal plate 22 (rolled plate made of 4N aluminum) that becomesa circuit layer 12, and a metal plate 23 (rolled plate made of 4Naluminum) that becomes a metal layer 13 are prepared.

Thereafter, Cu is adhered to both faces of the ceramics substrate 11 dueto a sputtering, and Cu-layers 24 and 25 having a film thickness of 0.15μm to 3 μm are thereby formed (Cu-adhering step).

Consequently, the ceramics substrate 11, the metal plates 22 and 23, andthe Cu-layers 24 and 25 are prepared.

Subsequently, as shown in FIG. 4B, the metal plate 22 is stacked on afirst face of the ceramics substrate 11, and the metal plate 23 isstacked on a second face of the ceramics substrate 11 (stacking step).

Therefore, a layered body 20 is formed.

Next, the layered body 20 that was formed in the above-described manneris heated in a state where the layered body 20 is pressed in the stackeddirection thereof (pressure is 1 to 5 kgf/cm²) and is set inside avacuum furnace.

Here, in the vacuum furnace, the degree of vacuum is 10⁻³ Pa to 10⁻⁵ Pa,and the heating temperature is 610° C. to 650° C.

Due to the pressing-heating step, as shown in FIG. 5B, surface layers ofthe metal plates 22 and 23, which become the circuit layer 12 and themetal layer 13, and the Cu-layers 24 and 25 are melted, and fusion metallayers 26 and 27 are formed on the surface of the ceramics substrate 11(melting step).

Subsequently, as shown in FIGS. 4C and 5C, by cooling the layered body20, the fusion metal layers 26 and 27 are solidified (solidifying step).

Due to the melting step and the solidifying step, Cu is diffused in thevicinity of the joint interface between the metal plate 22 that becomesthe circuit layer 12 and the ceramics substrate 11, or in the vicinityof the joint interface between the metal plate 23 that becomes the metallayer 13 and the ceramics substrate 11, so that the Cu concentration isin the range of 0.05 to 5 wt %.

In the above-described manner, the metal plates 22 and 23 that becomethe circuit layer 12 and the metal layer 13 are connected to theceramics substrate 11, and the power module substrate 10 of the firstembodiment is manufactured.

In the power module substrate 10 and the power module 1 of the firstembodiment having the above-described structure, Cu is diffused in thecircuit layer 12 (metal plate 22) and the metal layer 13 (metal plate23) in a solid-solution state.

In addition, since the Cu concentration in the joint interface 30between the circuit layer 12 and the ceramics substrate 11 or in thejoint interface 30 between the metal layer 13 and the ceramics substrate11 is in the range of 0.05 to 5 wt %, the joint interface 30 between thecircuit layer 12 (metal plate 22) and the metal layer 13 (metal plate23) is solid-solution strengthened.

Because of this, when a heat-load cycle or the like is performed, cracksare prevented from being propagated in the portions of the circuit layer12 (metal plate 22) and the metal layer 13 (metal plate 23), and it isthereby possible to considerably improve the reliability of the powermodule substrate 10 and the power module 1.

In addition, since the aluminum phase 41 in which Cu is diffused inaluminum, and the eutectic phase 42 composed of the binary eutecticstructure including Al and Cu are formed in the end portions in thewidth direction of the circuit layer 12 (metal plate 22) and the metallayer 13 (metal plate 23), it is possible to further strengthen the endportions in the width direction of the circuit layer 12 (metal plate 22)and the metal layer 13 (metal plate 23).

Consequently, it is possible to prevent fractures from being generatedat the end portions in the width direction of the circuit layer 12(metal plate 22) and the metal layer 13 (metal plate 23), and it ispossible to improve the junction reliability of the power modulesubstrate 10.

Furthermore, in the first embodiment, since precipitate particlescomposed of a compound including Cu (for example, CuAl₂) precipitate inthe eutectic phase 42, it is possible to realize precipitationstrengthening of the end portions in the width direction of the circuitlayer 12 (metal plate 22) and the metal layer 13 (metal plate 23), andit is possible to reliably prevent cracks from being propagated in theend portions in the width direction of the circuit layer 12 (metal plate22) and the metal layer 13 (metal plate 23).

In addition, in the center portion in the width direction of the jointinterface 30 between the ceramics substrate 11 and the circuit layer 12(metal plate 22), and in the center portion (portion A in FIG. 1) in thewidth direction of the joint interface 30 between the ceramics substrate11 and the metal layer 13 (metal plate 23), Cu is diffused in thecircuit layer 12 (metal plate 22) and in the metal layer 13 (metal plate23) in a solid-solution state, and a concentration-gradient layer 33 isformed in which the Cu concentration gradually decreases with increasesin the distance from the joint interface 30 in a stacked direction;furthermore, the soft layer 34 which has a Cu concentration lower thanthe Cu concentration in the near joint interface 30, which has a lowdegree of hardness, and which has a deformation resistance, is formed atthe opposite side of the ceramics substrate 11 in theconcentration-gradient layer 33 (lower side in FIG. 2).

In this structure, due to the soft layer 34, it is possible to absorbheat strain (heat stress) which is caused by the difference of thecoefficient of thermal expansion between the circuit layer 12 (metalplate 22) and the ceramics substrate 11 and by the difference of thecoefficient of thermal expansion between the metal layer 13 (metal plate23) and the ceramics substrate 11, and it is possible to considerablyimprove the heat-load cycle reliability of the power module substrate10.

According to the method for manufacturing a power module substrate ofthe first embodiment, since the ceramics substrate 11, the metal plate22 that becomes the circuit layer 12, and the metal plate 23 thatbecomes the metal layer 13 are stacked in layers with the Cu-layers 24and 25 interposed therebetween, and the ceramics substrate 11 and themetal plates 22 and 23 which were stacked in layers are pressed in thestacked direction and heated, the melting point of the near jointinterface 30 is lowered due to the eutectic reaction of Cu included inthe Cu-layers 24 and 25 and Al included in the metal plates 22 and 23.Therefore, even under relatively low-temperature, it is possible to formthe fusion metal layers 26 and 27 at the boundary face between theceramics substrate 11 and the metal plates 22 and 23, and it is possibleto connect the ceramics substrate 11 to the metal plates 22 and 23.

Since it is possible to connect the ceramics substrate 11 to the metalplates 22 and 23 without using a brazing filler metal composed of Al—Sialloy or the like in the above-described manner, there is not a concernthat a brazing filler metal penetrates to a surface of the circuit layer12, and it is possible to prevent the Ni-plating formed on the surfaceof the circuit layer 12 from peeling.

Consequently, it is possible to reliably form the solder layer 2 on thecircuit layer 12 with the Ni-plating interposed therebetween.

In addition, since the thickness of the Cu-layers 24 and 25 is 0.15 μmto 3 μm, the fusion metal layers 26 and 27 are reliably formed at theboundary face between the ceramics substrate 11 and the metal plates 22and 23, and it is possible to connect the ceramics substrate 11 to themetal plates 22 and 23.

In addition, it is possible to prevent reactants of Cu and Al from beingexcessively generated at the near joint interface 30, and it is possibleto prevent cracks from being generated in the ceramics substrate 11 whenthe ceramics substrate 11 is subjected to a heat-load cycle.

Furthermore, since the Cu-layers 24 and 25 are formed on the first faceand the second face of the ceramics substrate 11 (i.e., connection face,faces opposed to the metal plates 22 and 23), respectively, in theCu-adhering step in which Cu is adhered thereto by a sputtering, it ispossible to reliably stack the ceramics substrate 11 and the metalplates 22 and 23 in layers with the Cu-layers 24 and 25 interposedtherebetween, the ceramics substrate 11 is reliably bonded to the metalplates 22 and 23, and it is thereby possible to manufacture the powermodule substrate 10 of the first embodiment.

As described above, the first embodiment of the present invention isdescribed, the technical scope of the present invention is not limitedto the above embodiment, and various modifications may be made withoutdeparting from the scope of the present invention.

In the first embodiment of the present invention, the manufacturingmethod is described having the Cu-adhering step in which Cu is adheredto a surface of the ceramics substrate, it is not limited to thismethod, Cu may be adhered to a face of the metal plate facing to theceramics substrate 11 (connection face).

In addition, in the stacking step, the Cu-layer may be formed byinserting a copper foil between the ceramics substrate and the metalplate.

In addition, the method for forming the Cu-layer by a sputtering methodis described, it is not limited to this method, Cu may be adheredthereto by an evaporation method, a plating method, a method of applyinga paste, or the like.

Second Embodiment

FIG. 8 shows a power module substrate 60 and a power module 51 of asecond embodiment of the present invention.

In the second embodiment, identical symbols are used for the elementswhich are identical to those of the first embodiment, and theexplanations thereof are omitted or simplified.

The power module 51 includes a power module substrate 60 on which acircuit layer 62 is disposed, a semiconductor chip 3 which is bonded toa top face of the circuit layer 62 with a solder layer 2 interposedtherebetween, and a heatsink 4.

The power module substrate 60 includes a ceramics substrate 61, thecircuit layer 62 that is disposed on a first face of the ceramicssubstrate 61 (upper face in FIG. 8) and a metal layer 63 that isdisposed on a second face of the ceramics substrate 61 (lower face inFIG. 8).

The ceramics substrate 61 is a substrate used for preventing anelectrical connection between the circuit layer 62 and the metal layer63, and is made of AlN (aluminum nitride) with a high level ofinsulation.

In addition, the thickness of the ceramics substrate 61 is in a range of0.2 to 1.5 mm, and is 0.635 mm in the second embodiment.

By connecting a metal plate 72 having a conductive property to the firstface of the ceramics substrate 61, the circuit layer 62 is formed.

In the second embodiment, by connecting the metal plate 72 constitutedof a rolled plate composed of aluminum having a purity of 99.99% or more(a so-called 4N aluminum) to the ceramics substrate 61, the circuitlayer 62 is formed thereon.

By connecting a metal plate 73 to the second face of the ceramicssubstrate 61, the metal layer 63 is formed.

In the second embodiment, due to connecting the metal plate 73constituted of a rolled plate composed of aluminum having a purity of99.99% or more (a so-called 4N aluminum) to the ceramics substrate 61,the metal layer 63 is formed in a manner similar to the circuit layer62.

Consequently, when the joint interface 80 between the ceramics substrate61 and the circuit layer 62 (metal plate 72) and the joint interface 80between the ceramics substrate 61 and the metal layer 63 (metal plate73) are observed using a transmission electron microscope, a high-Cuconcentration section 82 in which Cu is concentrated is formed at thejoint interface 80 as shown in FIG. 9.

The Cu concentration in the high-Cu concentration section 82 is morethan the Cu concentrations in the circuit layer 62 (metal plate 72) andin the metal layer 63 (metal plate 73).

Specifically, the Cu concentration in the joint interface 80 is morethan twice the Cu concentrations in the circuit layer 62 and in themetal layer 63.

Here, in the second embodiment, the thickness H of the high-Cuconcentration section 82 is less than or equal to 4 nm.

Furthermore, the oxygen concentration in the high-Cu concentrationsection 82 is greater than the oxygen concentrations in the circuitlayer 62 and in the metal layer 63.

Here, in the joint interface 80 that is observed by a transmissionelectron microscope, the center between an end portion of the boundaryface of the grid image of the circuit layer 62 (metal plate 72) and themetal layer 63 (metal plate 73), and an end portion of the boundary faceof the grid image of the ceramics substrate 61, is defined as referenceface S as shown in FIG. 9.

In addition, the Cu concentrations and the oxygen concentrations in thecircuit layer 62 (metal plate 72) and in the metal layer 63 (metal plate73) mean the Cu concentrations and the oxygen concentrations at thepositions that are separated from the joint interface 80 by apredetermined distance (50 nm or more in the second embodiment) in thecircuit layer 62 (metal plate 72) or the metal layer 63 (metal plate73).

In addition, when the joint interface 80 is analyzed by energydispersive X-ray spectroscopy (EDS), the mass ratio of Al, Cu, O, and Nis in the range of Al:Cu:O:N=50 to 90 wt %:1 to 10 wt %:2 to 20 wt %:25wt % or less.

In addition, when the analyzation is performed by the EDS, the diameterof the spot therefor is 1 to 4 nm, a plurality of points (for example,100 points in the second embodiment) is measured at the joint interface80, and the average value thereof is calculated.

In addition, the joint interface 80 between the crystalline grain of themetal plates 72 and 73 constituting the circuit layer 62 and the metallayer 63, and the ceramics substrate 61 is only measured, and the jointinterface 80 between the crystalline grain boundary of the metal plates72 and 73 constituting the circuit layer 62 and the metal layer 63, andthe ceramics substrate 61 is not measured.

The foregoing power module substrate 60 is manufactured as describedbelow.

As shown in FIGS. 10A and 11A, the ceramics substrate 61 composed ofAlN, a metal plate 72 (rolled plate made of 4N aluminum) that becomes acircuit layer 62, a copper foil 74 having a thickness of 0.15 μm to 3 μm(3 μm in the second embodiment), a metal plate 73 (rolled plate made of4N aluminum) that becomes a metal layer 63, and a copper foil 75 havinga thickness of 0.15 μm to 3 μm (3 μm in the second embodiment) areprepared.

Next, as shown in FIGS. 10B and 11B, the metal plate 72 is stacked on afirst face of the ceramics substrate 61 with the copper foil 74interposed therebetween, and the metal plate 73 is stacked on a secondface of the ceramics substrate 61 with the copper foil 75 interposedtherebetween.

Consequently, a layered body 70 is formed.

Next, the layered body 70 is heated in a state where the layered body 70is pressed in the stacked direction thereof (pressure is 1 to 5 kgf/cm²)and is set inside a vacuum furnace (pressing-heating step).

Here, in the vacuum furnace, the degree of vacuum is 10⁻³ Pa to 10⁻⁵ Pa,and the heating temperature is 610° C. to 650° C.

Due to the pressing-heating step, as shown in FIG. 11B, the surfacelayers of metal plates 72 and 73 that become the circuit layer 62 andthe metal layer 63 are melted with the copper foils 74 and 75, andfusion aluminum layers 76 and 77 are formed on the surface (the firstface and the second face) of the ceramics substrate 61.

Subsequently, as shown in FIGS. 10C and 11C, by cooling the layered body70, the fusion aluminum layers 76 and 77 are solidified (solidifyingstep).

Due to the pressing-heating step and the solidifying step, a high-Cuconcentration section 82 having a Cu concentration and an oxygenconcentration that are greater than the Cu concentrations and the oxygenconcentrations in the metal plates 72 and 73 constituting the circuitlayer 62 and the metal layer 63 is generated in the joint interface 80.

In the above-described manner, a power module substrate 60 of the secondembodiment is manufactured.

In the power module substrate 60 and the power module 51 having theabove-described structure in the second embodiment, the high-Cuconcentration section 82 having a Cu concentration that is more thantwice the Cu concentrations in the circuit layer 62 and in the metallayer 63 is formed at the joint interface 80 between the circuit layer62, the metal layer 63, and the ceramics substrate 61; furthermore, theoxygen concentration in the high-Cu concentration section 82 is greaterthan the oxygen concentrations in the circuit layer 62 and in the metallayer 63.

Because of this, oxygen atom and Cu atom intervene in the jointinterface 80, and it is possible to improve the joint strength betweenthe ceramics substrate 61 composed of AlN and the circuit layer 62, andthe joint strength between the ceramics substrate 61 and the metal layer63.

Furthermore, in the second embodiment, when the joint interface 80 isanalyzed by energy dispersive X-ray spectroscopy, the mass ratio of Al,Cu, O, and N is in the range of Al:Cu:O:N=50 to 90 wt %:1 to 10 wt %:2to 20 wt %:25 wt % or less.

As a result, it is possible to prevent reactants of Cu and Alinterfering the joint from being excessively generated in the jointinterface 80, it is possible to sufficiently obtain the effect that thejoint strength is improved due to a Cu atom.

In addition, the thickness of a portion in which the oxygenconcentration is high is prevented from increasing in the jointinterface 80, and it is possible to suppress cracks from being generatedwhen a heat-load cycle is performed.

In addition, the metal plate 72 that becomes the circuit layer 62 isstacked on the first face of the ceramics substrate 61 composed of AlNwith the copper foil 74 having a thickness of 0.15 μm to 3 μm (3 μm inthe second embodiment) interposed therebetween, and the metal plate 73(rolled plate made of 4N aluminum) that becomes the metal layer 63 isstacked on the second face of the ceramics substrate 61 with the copperfoil 75 having a thickness of 0.15 μm to 3 μm (3 μm in the secondembodiment) interposed therebetween, and the layered body is pressed andheated.

As a result, eutectic reaction of Cu of the copper foils 74 and 75 andAl of the metal plates 72 and 73 is generated, and the melting point ofsurface layer portions between the copper foils 74 and 75, and the metalplates 72 and 73 is lowered.

Consequently, even under relatively low-temperatures (610° C. to 650°C.), it is possible to form the fusion aluminum layers 76 and 77 at theboundary face between the ceramics substrate 61 and the metal plates 72and 73, and it is possible to connect the ceramics substrate to themetal plate, and it is possible to connect the ceramics substrate 61 tothe metal plates 72 and 73.

Third Embodiment

Next, a third embodiment of the present invention will be described.

FIG. 12 shows a power module substrate 110 and a power module 101 of athird embodiment of the present invention.

In the third embodiment, identical symbols are used for the elementswhich are identical to those of the first and the second embodiments,and the explanations thereof are omitted or simplified.

The power module substrate 110 includes a ceramics substrate 111, thecircuit layer 112 that is disposed on a first face of the ceramicssubstrate 111 (upper face in FIG. 12) and a metal layer 113 that isdisposed on a second face of the ceramics substrate 111 (lower face inFIG. 12).

The ceramics substrate 111 is a substrate used for preventing anelectrical connection between the circuit layer 112 and the metal layer113, and is made of Si₃N₄ (silicon nitride) with a high level ofinsulation.

In addition, the thickness of the ceramics substrate 111 is in a rangeof 0.2 to 1.5 mm, and is 0.32 mm in the third embodiment.

By connecting a metal plate 122 having a conductive property to thefirst face of the ceramics substrate 111, the circuit layer 112 isformed.

In the third embodiment, by connecting the metal plate 22 constituted ofa rolled plate composed of aluminum having a purity of 99.99% or more (aso-called 4N aluminum) to the ceramics substrate 111, the circuit layer112 is formed thereon.

By connecting a metal plate 123 to the second face of the ceramicssubstrate 111, the metal layer 113 is formed.

In the third embodiment, due to connecting the metal plate 123constituted of a rolled plate composed of aluminum having a purity of99.99% or more (a so-called 4N aluminum) to the ceramics substrate 111,the metal layer 113 is formed in a manner similar to the circuit layer112.

Consequently, when the joint interface 130 between the ceramicssubstrate 111 and the circuit layer 112 (metal plate 122) and the jointinterface 130 between the ceramics substrate 111 and the metal layer 113(metal plate 123) are observed using a transmission electron microscope,a high-Cu concentration section 132 in which Cu is concentrated isformed at the joint interface 130 as shown in FIG. 13.

The Cu concentration in the high-Cu concentration section 132 is morethan the Cu concentrations in the circuit layer 112 (metal plate 122)and in the metal layer 113 (metal plate 123).

Specifically, the Cu concentration in the joint interface 130 is morethan twice the Cu concentrations in the circuit layer 112 and in themetal layer 113.

Here, in the third embodiment, the thickness H of the high-Cuconcentration section 132 is less than or equal to 4 nm.

Furthermore, the oxygen concentration in the high-Cu concentrationsection 132 is greater than the oxygen concentrations in the circuitlayer 112 and in the metal layer 113.

Here, in the joint interface 130 that is observed by a transmissionelectron microscope, the center between an end portion of the boundaryface of the grid image of the circuit layer 112 (metal plate 122) andthe metal layer 113 (metal plate 123), and an end portion of theboundary face of the grid image of the ceramics substrate 111, isdefined as reference face S as shown in FIG. 13.

In addition, the Cu concentrations and the oxygen concentrations in thecircuit layer 112 and in the metal layer 113 mean the Cu concentrationsand the oxygen concentrations at the positions that are separated fromthe joint interface 130 by a predetermined distance (50 nm or more inthe third embodiment) in the circuit layer 112 or the metal layer 13.

In addition, when the joint interface 130 is analyzed by energydispersive X-ray spectroscopy (EDS), the mass ratio of Al, Si, Cu, O,and N is in the range of Al:Si:Cu:O:N=15 to 45 wt %:15 to 45 wt %:1 to10 wt %:2 to 20 wt %:25 wt % or less.

In addition, when the analyzation is performed by the EDS, the diameterof the spot therefor is 1 to 4 nm, a plurality of points (for example,100 points in the third embodiment) is measured at the joint interface130, and the average value thereof is calculated.

In addition, the joint interface 130 between the crystalline grain ofthe metal plates 122 and 123 constituting the circuit layer 112 and themetal layer 113, and the ceramics substrate 111 is only measured, andthe joint interface 130 between the crystalline grain boundary of themetal plates 122 and 123 constituting the circuit layer 112 and themetal layer 113, and the ceramics substrate 111 is not measured.

The foregoing power module substrate 110 is manufactured as describedbelow.

As shown in FIG. 14A, Cu is adhered to the both faces of the ceramicssubstrate 111 composed of Si₃N₄ by a vacuum deposition method, andCu-adhesion layers 124 and 125 having a thickness of 0.15 μm to 3 μm areformed (Cu-adhering step).

Next, as shown in FIGS. 14B and 14C, and FIGS. 15A and 15B, the metalplate 122 (rolled plate made of 4N aluminum) that becomes the circuitlayer 112 is stacked on the first face of the ceramics substrate 111 onwhich the Cu-adhesion layers 124 and 125 are formed, and the metal plate123 (rolled plate made of 4N aluminum) that becomes the metal layer 113is stacked on the second face of the ceramics substrate 111 (stackingstep).

The layered body 120 that was formed in the above-described manner isheated in a state where the layered body 120 is pressed in the stackeddirection thereof (pressure is 1 to 5 kgf/cm²) and is set inside avacuum furnace (pressing-heating step).

Here, in the vacuum furnace, the degree of vacuum is 10⁻³ Pa to 10⁻⁵ Pa,and the heating temperature is 610° C. to 650° C.

Due to the pressing-heating step, as shown in FIG. 15, the surfacelayers of metal plates 122 and 123 that become the circuit layer 112 andthe metal layer 113 are melted with the Cu-adhesion layers 124 and 125,and fusion aluminum layers 126 and 127 are formed on the surface of theceramics substrate 111.

Subsequently, as shown in FIGS. 14D and 15C, by cooling the layered body120, the fusion aluminum layers 126 and 127 are solidified (solidifyingstep).

Due to the pressing-heating step and the solidifying step, a high-Cuconcentration section 132 having a Cu concentration and an oxygenconcentration that are greater than the Cu concentrations and the oxygenconcentrations in the metal plates 122 and 123 constituting the circuitlayer 112 and the metal layer 113 is generated in the joint interface130.

In the above-described manner, a power module substrate 110 of the thirdembodiment is manufactured.

In the power module substrate 110 having the above-described structurein the third embodiment, the high-Cu concentration section 132 having aCu concentration that is more than twice the Cu concentrations in thecircuit layer 112 and in the metal layer 113 is formed at the jointinterface 130 between the circuit layer 112, the metal layer 113, andthe ceramics substrate 111.

Furthermore, the oxygen concentration in the high-Cu concentrationsection 132 is greater than the oxygen concentrations in the circuitlayer 112 and in the metal layer 113.

Because of this, oxygen atom and Cu atom intervene in the jointinterface 130, and it is possible to improve the joint strength betweenthe ceramics substrate 111 composed of Si₃N₄, the circuit layer 112, andthe metal layer 113.

Furthermore, in the third embodiment, since the mass ratio of Al, Si,Cu, O, and N is in the range of Al:Si:Cu:O:N=15 to 45 wt %:15 to 45 wt%:1 to 10 wt %:2 to 20 wt %:25 wt % or less when the joint interface 130is analyzed by energy dispersive X-ray spectroscopy (EDS), it ispossible to prevent reactants of Cu and Al interfering the joint frombeing excessively generated in the joint interface 130, it is possibleto sufficiently obtain the effect that the joint strength is improveddue to a Cu atom.

In addition, the thickness of a portion in which the oxygenconcentration is high is prevented from increasing in the jointinterface 130, and it is possible to suppress cracks from beinggenerated when a heat-load cycle is performed.

In addition, Cu is adhered to the both faces of the ceramics substrate111 composed of Si₃N₄ by a vacuum deposition method, and the metal plate122 (rolled plate made of 4N aluminum) that becomes the circuit layer112 is stacked on the first face of the ceramics substrate 111 on whichthe Cu-adhesion layers 124 and 125 are formed, and the metal plate 123(rolled plate made of 4N aluminum) that becomes the metal layer 113 isstacked on the second face of the ceramics substrate 111, and thelayered body is pressed and heated.

As a result, due to the eutectic reaction of Cu of Cu-adhesion layers124 and 125 and Al of the metal plates 122 and 123, the melting point ofthe surface layer portions of the metal plates 122 and 123 is lowered,even under relatively low-temperatures (610° C. to 650° C.), it ispossible to form the fusion aluminum layers 126 and 127 at the boundaryface between the ceramics substrate 111 and the metal plates 122 and123, and it is possible to connect the ceramics substrate 111 to themetal plates 122 and 123.

As described above, the second and the third embodiments of the presentinvention are described, the technical scope of the present invention isnot limited to the above embodiment, and various modifications may bemade without departing from the scope of the present invention.

In the third embodiment, the manufacturing method is described foradhering Cu to the both-faces of the ceramics substrate, it is notlimited to this method, Cu may be adhered to a face of the metal platefacing to the ceramics substrate 11 (connection face), and Cu may beadhered to both of the metal plate and the ceramics substrate.

In addition, the method for adhering Cu by a vacuum deposition method isdescribed, it is not limited to this method, Cu may be adhered theretoby a sputtering method, a plating method, a method of applying aCu-paste, or the like.

Fourth Embodiment

FIG. 20 shows a power module substrate 160 and a power module 151 of afourth embodiment of the present invention.

In the fourth embodiment, identical symbols are used for the elementswhich are identical to those of the first to the third embodiments, andthe explanations thereof are omitted or simplified.

The power module 151 includes a power module substrate 160 on which acircuit layer 162 is disposed, a semiconductor chip 3 which is bonded toa top face of the circuit layer 162 with a solder layer 2 interposedtherebetween, and a heatsink 4.

The power module substrate 160 includes a ceramics substrate 161, thecircuit layer 162 that is disposed on a first face of the ceramicssubstrate 161 (upper face in FIG. 20) and a metal layer 163 that isdisposed on a second face of the ceramics substrate 161 (lower face inFIG. 20).

The ceramics substrate 161 is a substrate used for preventing anelectrical connection between the circuit layer 162 and the metal layer163, and is made of Al₂O₃ (alumina) with a high level of insulation.

In addition, the thickness of the ceramics substrate 161 is in a rangeof 0.2 to 1.5 mm, and is 0.635 mm in the fourth embodiment.

By connecting a metal plate 172 having a conductive property to thefirst face of the ceramics substrate 161, the circuit layer 162 isformed.

In the fourth embodiment, by connecting the metal plate 172 constitutedof a rolled plate composed of aluminum having a purity of 99.99% or more(a so-called 4N aluminum) to the ceramics substrate 161, the circuitlayer 162 is formed thereon.

By connecting a metal plate 173 to the second face of the ceramicssubstrate 161, the metal layer 163 is formed.

In the fourth embodiment, due to connecting the metal plate 173constituted of a rolled plate composed of aluminum having a purity of99.99% or more (a so-called 4N aluminum) to the ceramics substrate 161,the metal layer 163 is formed in a manner similar to the circuit layer162.

Consequently, when the joint interface 180 between the ceramicssubstrate 161 and the circuit layer 162 (metal plate 172) and the jointinterface 180 between the ceramics substrate 161 and the metal layer 163(metal plate 173) are observed using a transmission electron microscope,a high-Cu concentration section 182 in which Cu is concentrated isformed at the joint interface 180 as shown in FIG. 21.

The Cu concentration in the high-Cu concentration section 182 is morethan the Cu concentrations in the circuit layer 162 (metal plate 172)and in the metal layer 163 (metal plate 173).

Specifically, the Cu concentration in the joint interface 180 is morethan twice the Cu concentrations in the circuit layer 162 and in themetal layer 163.

Here, in the fourth embodiment, the thickness H of the high-Cuconcentration section 182 is less than or equal to 4 nm.

Here, in the joint interface 180 that is observed by a transmissionelectron microscope, the center between an end portion of the boundaryface of the grid image of the circuit layer 162 (metal plate 172) andthe metal layer 163 (metal plate 173), and an end portion of theboundary face of the grid image of the ceramics substrate 161, isdefined as reference face S as shown in FIG. 21.

In addition, the Cu concentrations in the circuit layer 162 (metal plate172) and in the metal layer 163 (metal plate 173) mean the Cuconcentrations at the positions that are separated from the jointinterface 180 by a predetermined distance (50 nm or more in the fourthembodiment) in the circuit layer 162 (metal plate 172) or the metallayer 163 (metal plate 173).

In addition, when the joint interface 180 is analyzed by energydispersive X-ray spectroscopy (EDS), the mass ratio of Al, Cu, and O isin the range of Al:Cu:O=50 to 90 wt %:1 to 10 wt %:0 to 45 wt %.

In addition, when the analyzation is performed by the EDS, the diameterof the spot therefor is 1 to 4 nm, a plurality of points (for example,100 points in the fourth embodiment) is measured at the joint interface180, and the average value thereof is calculated.

In addition, the joint interface 180 between the crystalline grain ofthe metal plates 172 and 173 constituting the circuit layer 162 and themetal layer 163, and the ceramics substrate 161 is only measured, andthe joint interface 180 between the crystalline grain boundary of themetal plates 172 and 173 constituting the circuit layer 162 and themetal layer 163, and the ceramics substrate 161 is not measured.

The foregoing power module substrate 160 is manufactured as describedbelow.

As shown in FIGS. 22A and 23A, the ceramics substrate 161 composed ofAl₂O₃, a metal plate 172 (rolled plate made of 4N aluminum) that becomesa circuit layer 162, a copper foil 174 having a thickness of 0.15 μm to3 μm (3 μm in the fourth embodiment), a metal plate 173 (rolled platemade of 4N aluminum) that becomes a metal layer 163, and a copper foil175 having a thickness of 0.15 μm to 3 μm (3 μm in the fourthembodiment) are prepared.

Next, as shown in FIGS. 22B and 23B, the metal plate 172 is stacked on afirst face of the ceramics substrate 161 with the copper foil 174interposed therebetween, and the metal plate 173 is stacked on a secondface of the ceramics substrate 161 with the copper foil 175 interposedtherebetween.

Consequently, a layered body 170 is formed.

Next, the layered body 170 is heated in a state where the layered body170 is pressed in the stacked direction thereof (pressure is 1 to 5kgf/cm²) and is set inside a vacuum furnace (pressing-heating step).

Here, in the vacuum furnace, the degree of vacuum is 10⁻³ Pa to 10⁻⁵ Pa,and the heating temperature is 610° C. to 650° C.

Due to the pressing-heating step, as shown in FIG. 23, the surfacelayers of metal plates 172 and 173 that become the circuit layer 162 andthe metal layer 163 are melted with the copper foils 174 and 175, andfusion aluminum layers 176 and 177 are formed on the surface of theceramics substrate 161.

Subsequently, as shown in FIGS. 22C and 23C, by cooling the layered body170, the fusion aluminum layers 176 and 177 are solidified (solidifyingstep).

Due to the pressing-heating step and the solidifying step, a high-Cuconcentration section 182 having a Cu concentration that is greater thanthe Cu concentrations in the metal plates 172 and 173 constituting thecircuit layer 162 and the metal layer 163 is generated in the jointinterface 180.

In the above-described manner, a power module substrate 160 of thefourth embodiment is manufactured.

In the power module substrate 160 and the power module 151 having theabove-described structure in the fourth embodiment, the high-Cuconcentration section 182 having a Cu concentration that is more thantwice the Cu concentrations in the circuit layer 162 and in the metallayer 163 is formed at the joint interface 180 between the circuit layer162, the metal layer 163, and the ceramics substrate 161.

Because of this, Cu atom intervenes in the joint interface 180, and itis possible to improve the joint strength between the ceramics substrate161 composed of Al₂O₃ and the circuit layer 162, and the joint strengthbetween the ceramics substrate 161 and the metal layer 163.

Furthermore, in the fourth embodiment, when the joint interface 180 isanalyzed by energy dispersive X-ray spectroscopy, the mass ratio of Al,Cu, and O is in the range of Al:Cu:O=50 to 90 wt %:1 to 10 wt %:0 to 45wt %.

As a result, it is possible to prevent reactants of Cu and Alinterfering the joint from being excessively generated in the jointinterface 180, it is possible to sufficiently obtain the effect that thejoint strength is improved due to a Cu atom.

In addition, the metal plate 172 that becomes the circuit layer 162 isstacked on the first face of the ceramics substrate 161 composed ofAl₂O₃ with the copper foil 174 having a thickness of 0.15 μm to 3 μm (3μm in the fourth embodiment) interposed therebetween, and the metalplate 173 (rolled plate made of 4N aluminum) that becomes the metallayer 163 is stacked on the second face of the ceramics substrate 161with the copper foil 175 having a thickness of 0.15 μm to 3 μm (3 μm inthe fourth embodiment) interposed therebetween, and the layered body ispressed and heated.

As a result, eutectic reaction of Cu of the copper foils 174 and 175 andAl of the metal plates 172 and 173 is generated, and the melting pointof surface layer portions between the copper foils 174 and 175, and themetal plates 172 and 173 is lowered.

Consequently, even under relatively low-temperatures (610° C. to 650°C.), it is possible to form the fusion aluminum layers 176 and 177 atthe boundary face between the ceramics substrate 161 and the metalplates 172 and 173, and it is possible to connect the ceramics substrateto the metal plate, and it is possible to connect the ceramics substrate161 to the metal plates 172 and 173.

As described above, the fourth embodiment of the present invention isdescribed, the technical scope of the present invention is not limitedto the above embodiment, and various modifications may be made withoutdeparting from the scope of the present invention.

In the fourth embodiment of the present invention, the method forinserting the copper foil between the ceramics substrate and the metalplate in the stacking step, it is not limited to this method, before thestacking step, a Cu-layer may be formed by a Cu-adhering step foradhering Cu to at least one of a face of the metal plate (connectionface) opposed to the ceramics substrate and a face of the ceramicssubstrate (connection face) opposed to the metal plate.

In addition, as a method for adhering Cu, for example, a vacuumdeposition method, a sputtering method, a plating method, a method ofapplying a Cu-paste, or the like may be adopted.

Fifth Embodiment

FIG. 26 shows a power module substrate and a power module of a fifthembodiment of the present invention.

In the fifth embodiment, identical symbols are used for the elementswhich are identical to those of the first to the fourth embodiments, andthe explanations thereof are omitted or simplified.

The power module 201 includes a power module substrate 210 on which acircuit layer 212 is disposed, a semiconductor chip 3 which is bonded toa top face of the circuit layer 212 with a solder layer 2 interposedtherebetween, and a heatsink 4.

The power module substrate 210 includes a ceramics substrate 211, thecircuit layer 212 that is disposed on a first face of the ceramicssubstrate 211 (upper face in FIG. 26) and a metal layer 213 that isdisposed on a second face of the ceramics substrate 211 (lower face inFIG. 26).

The ceramics substrate 211 is a substrate used for preventing anelectrical connection between the circuit layer 212 and the metal layer213, and is made of AlN (aluminum nitride) with a high level ofinsulation.

In addition, the thickness of the ceramics substrate 211 is in a rangeof 0.2 to 1.5 mm, and is 0.635 mm in the fifth embodiment.

In addition, as shown in FIG. 26, the width of the ceramics substrate211 is greater than the widths of the circuit layer 212 and the metallayer 213 in the fifth embodiment.

By connecting a metal plate 222 having a conductive property to thefirst face of the ceramics substrate 211, the circuit layer 212 isformed.

In the fifth embodiment, by connecting the metal plate 222 constitutedof a rolled plate composed of aluminum having a purity of 99.99% or more(a so-called 4N aluminum) to the ceramics substrate 211, the circuitlayer 212 is formed thereon.

Here, an Al—Si system brazing filler metal including Si that is amelting-point lowering element is used for connecting the ceramicssubstrate 211 to the metal plate 222.

By connecting a metal plate 223 to the second face of the ceramicssubstrate 211, the metal layer 213 is formed.

In the fifth embodiment, due to connecting the metal plate 223constituted of a rolled plate composed of aluminum having a purity of99.99% or more (a so-called 4N aluminum) to the ceramics substrate 211,the metal layer 213 is formed in a manner similar to the circuit layer212.

Here, an Al—Si system brazing filler metal including Si that is amelting-point lowering element is used for connecting the ceramicssubstrate 211 to the metal plate 223.

Consequently, as shown in FIG. 27, in the center portion in the widthdirection of the joint interface 230 between the ceramics substrate 211and the circuit layer 212 (metal plate 222), and in the center portion(portion A in FIG. 26) in the width direction of the joint interface 230between the ceramics substrate 211 and the metal layer 213 (metal plate223), Si and Cu are diffused in the circuit layer 212 (metal plate 222)and in the metal layer 213 (metal plate 223), and aconcentration-gradient layer 233 is formed in which the Si concentrationand the Cu concentration gradually decrease with increasing the distancefrom the joint interface 230 in a stacked direction.

Here, in the portion which is close to the joint interface 230 of theconcentration-gradient layer 233, the Si concentration is in the rangeof 0.05 to 0.5 wt % wt %, and the Cu concentration is in the range of0.05 to 1.0 wt %.

In addition, the Si concentration and the Cu concentration in theportion which is close to the joint interface 230 of theconcentration-gradient layer 233 is the average value of five pointswhich are measured in the range from the joint interface 230 to 50 μm byuse of an EPMA analyzation (diameter of spot is 30 μm).

In addition, in the end portion 235 in the width direction of the jointinterface 230 between the ceramics substrate 211 and the circuit layer212 (metal plate 222), and in the end portion 235 (portion B in FIG. 26)in the width direction of the joint interface 230 between the ceramicssubstrate 211 and the metal layer 213 (metal plate 223), as shown inFIG. 28, an aluminum phase 241 in which Si and Cu are diffused inaluminum in a solid-solution state, a Si phase 242 in which the contentrate of Si is greater than or equal to 98 wt %, and an eutectic phase243 composed of a ternary eutectic structure including Al, Cu, and Siare formed.

In addition, precipitate particles composed of a compound including Cu(for example, CuAl₂) precipitate in the eutectic phase 243.

In addition, when the joint interface 230 between the ceramics substrate211 and the circuit layer 212 (metal plate 222) and the joint interface230 between the ceramics substrate 211 and the metal layer 213 (metalplate 223) are observed using a transmission electron microscope, ahigh-Si concentration section 232 in which Si is concentrated is formedat the joint interface 230 as shown in FIG. 29.

The Si concentration in the high-Si concentration section 232 is morethan five times the Si concentrations in the circuit layer 212 (metalplate 222) and in the metal layer 213 (metal plate 223).

In addition, the thickness H of the high-Si concentration section 232 isless than or equal to 4 nm.

Here, in the joint interface 230 that is observed by a transmissionelectron microscope, the center between an end portion of the boundaryface of the grid image of the circuit layer 212 (metal plate 222) andthe metal layer 213 (metal plate 223), and an end portion of theboundary face of the grid image of the ceramics substrate 211, isdefined as reference face S as shown in FIG. 29.

The foregoing power module substrate 210 is manufactured as describedbelow.

At first, Cu is adhered to the both faces of the ceramics substrate 211composed of AlN by a sputtering method (Cu-adhering step).

Subsequently, as shown in FIGS. 30A and 31A, the ceramics substrate 211composed of AlN to which was Cu was adhered, a metal plate 222 (rolledplate made of 4N aluminum) that becomes a circuit layer 212, a brazingfiller metal foil 224 having a thickness of 10 to 30 μm (20 μm in thefifth embodiment), a metal plate 223 (rolled plate made of 4N aluminum)that becomes a metal layer 213, and a brazing filler metal foil 225having a thickness of 10 to 30 μm (20 μm in the fifth embodiment) areprepared.

Next, as shown in FIGS. 30B and 31B, the metal plate 222 is stacked on afirst face of the ceramics substrate 211 with the brazing filler metalfoil 224 interposed therebetween, and the metal plate 223 is stacked ona second face of the ceramics substrate 211 with the brazing fillermetal foil 225 interposed therebetween (stacking step).

Therefore, a layered body 220 is formed.

Next, the layered body 220 is heated in a state where the layered body220 is pressed in the stacked direction thereof (pressure is 1 to 5kgf/cm²) and is set inside a vacuum furnace, and the brazing fillermetal foils 224 and 225 are melted (melting step).

Here, the degree of vacuum is 10⁻³ Pa to 10⁻⁵ Pa in the vacuum furnace.

Due to the melting step, as shown in FIG. 31B, a part of the metalplates 222 and 223, which become the circuit layer 212 and the metallayer 213, and the brazing filler metal foils 224 and 225 are melted,and fusion aluminum layers 226 and 227 are formed on the surface of theceramics substrate 211.

Subsequently, as shown in Figures. FIGS. 30C and 31C, by cooling thelayered body 220, the fusion metal layers 226 and 227 are solidified(solidifying step).

In the above-described manner, the metal plates 222 and 223 that becomethe circuit layer 212 and the metal layer 213 are connected to theceramics substrate 211, and the power module substrate 210 of the fifthembodiment is manufactured.

In the power module substrate 210 and the power module 201 of the fifthembodiment having the above-described structure, the circuit layer 212(metal plate 222) and the metal layer 213 (metal plate 223) areconnected to the ceramics substrate 211 by use of the Al—Si systembrazing filler metal, and Cu is introduced into the joint interface 230between the circuit layer 212 (metal plate 222), the metal layer 213(metal plate 223), and the ceramics substrate 211.

Consequently, Cu and Al existing at the joint interface 230 are meltedand reacted, even if the connecting is performed under the junctioncondition where a temperature is relatively low in a short time, it ispossible to tightly connect the ceramics substrate 211 to the circuitlayer 212 (metal plate 222) and the metal layer 213 (metal plate 223),and it is possible to considerably improve junction reliability.

In addition, in the center portion in the width direction of the jointinterface 230 between the ceramics substrate 211 and the circuit layer212 (metal plate 222), and in the center portion (portion A in FIG. 26)in the width direction of the joint interface 230 between the ceramicssubstrate 211 and the metal layer 213 (metal plate 223), Si and Cu arediffused in the circuit layer 212 (metal plate 222) and in the metallayer 213 (metal plate 223), and a concentration-gradient layer 233 isformed in which the Si concentration and the Cu concentration graduallydecrease with increasing the distance from the joint interface 230 in astacked direction.

In addition, since the Cu concentration in the portion of theconcentration-gradient layer 233 which is close to the joint interface230 is in the range of 0.05 to 1.0 wt %, the portions of the circuitlayer 212 (metal plate 222) and the metal layer 213 (metal plate 223)which are close to the joint interface 230 are solid-solutionstrengthened, it is possible to prevent fractures from being generatedat the circuit layer 212 (metal plate 222) and the metal layer 213(metal plate 223).

In addition, since the Si concentration in the portion of theconcentration-gradient layer 233 which is close to the joint interface230 is in the range of 0.05 to 0.5 wt %, Si is sufficiently diffused inthe circuit layer 212 (metal plate 222) and the metal layer 213 (metalplate 223).

For this reason, since the brazing filler metal is reliably melted andsolidified, it is possible to tightly connect the ceramics substrate 211to the circuit layer 212 (metal plate 222), and connect the ceramicssubstrate 211 to the metal layer 213 (metal plate 223).

Furthermore, the width of the ceramics substrate 211 is greater than thewidths of the circuit layer 212 (metal plate 222) and the metal layer213 (metal plate 223); the aluminum phase 241 in which Si and Cu arediffused in aluminum, the Si phase 242 in which the content rate of Siis greater than or equal to 98 wt %, and the eutectic phase 243 composedof a ternary eutectic structure including Al, Cu, and Si are formed atthe end portion 235 in the width direction of the circuit layer 212(metal plate 222) and the metal layer 213 (metal plate 223).

Consequently, the strength of the end portion 235 in the width directionof the circuit layer 212 (metal plate 222) and the metal layer 213(metal plate 223) is improved.

Furthermore, since precipitate particles composed of a compoundincluding Cu (for example, CuAl₂) precipitate in the eutectic phase 243,it is possible to further realize precipitation strengthening of the endportion 235 in the width direction.

As a result, it is possible to prevent fractures from being generated atthe end portion 235 in the width direction of the circuit layer 212(metal plate 222) and the metal layer 213 (metal plate 223).

In addition, in the fifth embodiment, the ceramics substrate 211 iscomposed of AlN, and the high-Si concentration section 232 having the Siconcentration that is more than five times the Si concentrations in thecircuit layer 212 (metal plate 222) and in the metal layer 213 (metalplate 223) is formed at the joint interface 230 between the metal plates222 and 223 and the ceramics substrate 211.

Because of this, due to Si existing at the joint interface 230, it ispossible to improve the joint strength between the ceramics substrate211 and the metal plates 222 and 223.

Sixth Embodiment

Next, a sixth embodiment of the present invention will be described withreference to FIGS. 32 and 33.

In the sixth embodiment, identical symbols are used for the elementswhich are identical to those of the first to the fifth embodiments, andthe explanations thereof are omitted or simplified.

The power module substrate 260 of the sixth embodiment is different fromthe fifth embodiment in terms of the ceramics substrate 261 beingcomposed of Si₃N₄.

Here, when the joint interface 280 between the ceramics substrate 261and the circuit layer 262 (metal plate 272) and the joint interface 280between the ceramics substrate 261 and the metal layer 263 (metal plate273) are observed using a transmission electron microscope, ahigh-oxygen concentration section 282 in which oxygen is concentrated isformed at the joint interface 280 is observed as shown in FIG. 33.

The oxygen concentration in the high-oxygen concentration section 282 isgreater than the oxygen concentrations in the circuit layer 262 (metalplate 272) and in the metal layer 263 (metal plate 273).

In addition, the thickness H of the high-oxygen concentration section282 is less than or equal to 4 nm.

Here, in the joint interface 280 that is observed by a transmissionelectron microscope, the center between an end portion of the boundaryface of the grid image of the circuit layer 262 (metal plate 272) andthe metal layer 263 (metal plate 273), and an end portion of the jointboundary face of the grid image of the ceramics substrate 261, isdefined as reference face S as shown in FIG. 33.

In the power module substrate 260 of the sixth embodiment having theabove-described structure, since the high-oxygen concentration section282 in which the oxygen concentration thereof is greater than the oxygenconcentrations in the metal plates 272 and 273 that constitute thecircuit layer 262 and the metal layer 263 is formed in the jointinterface 280 between the ceramics substrate 261 and the metal plates272 and 273 that become the circuit layer 262 and the metal layer 263,due to oxygen, it is possible to improve the joint strength between theceramics substrate 261 and the metal plates 272 and 273.

In addition, since the thickness of the high-oxygen concentrationsection 282 is less than or equal to 4 nm, generation of crack issuppressed in the high-oxygen concentration section 282 due to thestress when a heat-load cycle is performed.

As described above, the first to the sixth embodiments of the presentinvention are described, the technical scope of the present invention isnot limited to the above embodiment, and various modifications may bemade without departing from the scope of the present invention.

For example, the case where a rolled plate composed of aluminum having apurity of 99.99% is adopted as a metal plate constituting the circuitlayer and the metal layer is described, however, it is not limited tothis method, and aluminum having a purity of 99% (2N aluminum) may beused.

In addition, the case where the buffer layer composed of aluminum, analuminum alloy, or a combination of materials including aluminum (forexample, AlSiC or the like) is provided between the top panel section ofthe heatsink and the metal layer is described, however, it is notnecessary to provide the buffer layer.

Moreover, the structure in which the heatsink is formed of aluminum isdescribed, however, a structure in which the heatsink is formed of analuminum alloy, a composite material including aluminum, copper, acopper alloy or the like may be employed.

Furthermore, the structure having the flow passage of cooling medium asa heatsink is described, however, the structure of the heatsink is notlimited.

In addition, in the fifth embodiment, the case where the ceramicssubstrate composed of AlN is used is described, it is not limited tothis structure, and a ceramics composed of Al₂O₃ or the like may beused.

In addition, the manufacturing method is described having theCu-adhering step in which Cu is adhered to a surface of the ceramicssubstrate, it is not limited to this method, and Cu may be adhered to asurface of a brazing filler metal foil.

In addition, not only a sputtering method, but also Cu may be adheredthereto by an evaporation method, a plating method, or the like.

In addition, Cu may be introduced into an Al—Si system brazing fillermetal.

EXAMPLES

Next, the results of confirmatory experiments which were performed inorder to confirm the effectivity of the power module substrate (powermodule) of the above-described first to sixth embodiments are described.

Example 1

In the example 1 described below, with reference to FIGS. 6 and 7, theresults of confirmatory experiments which were performed in order toconfirm the effectivity of the power module substrate of the firstembodiment are described.

Firstly, as the power module substrate used for the experiment, a powermodule substrate was manufactured by the following method ofmanufacturing.

Specifically, a ceramics substrate composed of AlN having 40 mm squareand a thickness of 0.635 mm, and two metal plates composed of aluminum4N having a thickness of 0.6 mm were prepared.

Thereafter, Cu was adhered to the both faces of the ceramics substrateby a vacuum deposition, and a layered body was formed by stacking themetal plates on both faces of the ceramics substrate.

The layered body was heated in a vacuum furnace (the degree of vacuum is10⁻³ Pa to 10⁻⁵ Pa) in a state where a pressure of 1 to 5 kgf/cm² wasapplied thereto in a stacked direction, and a power module substrateprovided with a ceramics substrate, a circuit layer, and a metal layerwas manufactured.

In a way similar to the above-described manner, a ceramics substratecomposed of AlN having 40 mm of square and a thickness of 0.635 mm, andtwo metal plates composed of aluminum 4N having a thickness of 0.6 mmwere prepared.

Thereafter, Cu was adhered to one of the faces of each metal plate by avacuum deposition, the metal plate was stacked on the both faces of theceramics substrate so that the face of the metal plate on which theevaporation is performed faces the ceramics substrate, and thereby alayered body is formed.

The layered body was heated in a vacuum furnace (the degree of vacuum is10⁻³ Pa to 10⁻⁵ Pa) in a state where a pressure of 1 to 5 kgf/cm² wasapplied thereto in a stacked direction, and a power module substrateprovided with a ceramics substrate, a circuit layer, and a metal layerwas manufactured.

As described above, in the example 1, two kinds of power modulesubstrates were employed.

Here, adherence amounts of the adhered Cu (thickness of Cu) by vacuumdeposition were different from each other by five parameters (fivelevels), and were 0.1 μm, 0.5 μm, 1.0 μm, 2.0 μm, and 3.0 μm.

In addition, the heating temperatures were different from each other bythree parameters (three levels), and were 610° C., 630° C., and 650° C.

Consequently, a total of thirty kinds of power module substrates wereprepared.

An aluminum plate (A6063) was connected to the metal layer of the powermodule substrate that were formed in this manner with a buffer layercomposed of AlSiC and having a thickness of 0.9 mm interposedtherebetween, the aluminum plate corresponding to a top panel of aheatsink, and having lengths of 50 mm and 60 mm and a thickness of 5 mm.

Consequently, a total of thirty kinds of test pieces were prepared.

Subsequently, before the thirty kinds of test pieces being subjected toa heat-load cycle test, the percentage of connected-surface area(junction rate) in the joint interface between the ceramics substrateand the metal plate was determined.

Specifically, by use of an ultrasonic imaging device (frequency oftransducer is 15 MHz), the joint interface between the ceramicssubstrate and the metal plate was captured, the data that has beenobtained by the capturing was binarized, the junction rate wascalculated by obtaining the surface area of a bonded portion of theentirety of the joint interface.

In addition, the junction rate between a ceramics substrate and a metalplate was 100%, before a heat-load cycle test is performed.

Subsequently, a total of thirty kinds of test pieces were subjected toheat-load cycles of −40° C. to 105° C. by 3000 times under load.

Thereafter, by the same method as the above-described method in whichthe ultrasonic imaging device was used, the junction rate between aceramics substrate and a metal plate, that is, the junction rate afterthe 3000 heat-load cycles were performed, was determined.

As a result, evaluation results of the power module substrate wereobtained.

An evaluation result of the power module substrate that is obtained byevaporating and adhering Cu to the ceramics substrate is shown in FIG.6.

In addition, an evaluation result of the power module substrate that isobtained by evaporating and adhering Cu to the metal plate is shown inFIG. 7.

In addition, in FIGS. 6 and 7, the power module substrate is representedby the symbol “◯”, in which the junction rate was 85% or more after thepower module substrate is subjected to a 3000 cyclical thermal load; thepower module substrate is represented by the symbol “Δ”, in which thejunction rate was greater than or equal to 70% and less than 85% afterthe power module substrate is subjected to a 3000 cyclical thermal load;and the power module substrate is represented by the symbol “X”, inwhich the junction rate was less than 70% after the power modulesubstrate is subjected to a 3000 cyclical thermal load.

As shown in FIGS. 6 and 7, it was confirmed that, as the heatingtemperature increases, the junction reliability was improved.

In addition, in the case where the thickness of the Cu-layer isapproximately 1.0 μm to 2.0 μm, even if the heating temperature is low,it was confirmed that the junction reliability was improved.

Furthermore, FIGS. 6 and 7 shows the same tendency, it was not confirmedthat the difference between the case where Cu was adhered to theceramics substrate and the case where Cu was adhered to the metal plate.

Example 2

In the example 2 described below, with reference to FIGS. 16A, 16B, 17A,and 17B, the results of confirmatory experiments which were performed inorder to confirm the effectivity of the power module substrate of thesecond embodiment are described.

Firstly, as the power module substrate used for the experiment, a powermodule substrate was manufactured by the following method ofmanufacturing.

Specifically, a ceramics substrate composed of AlN having 40 mm squareand a thickness of 0.635 mm, and two metal plates composed of aluminum4N having a thickness of 0.6 mm were prepared.

Thereafter, Cu was adhered to the both faces of the ceramics substrateby a vacuum deposition, and a layered body was formed by stacking themetal plates on both faces of the ceramics substrate.

The layered body was heated in a vacuum furnace (the degree of vacuum is10⁻³ Pa to 10⁻⁵ Pa) in a state where a pressure of 1 to 5 kgf/cm² wasapplied thereto in a stacked direction, and a power module substrateprovided with a ceramics substrate, a circuit layer, and a metal layerwas manufactured.

In a way similar to the above-described manner, a ceramics substratecomposed of AlN having 40 mm of square and a thickness of 0.635 mm, andtwo metal plates composed of aluminum 4N having a thickness of 0.6 mmwere prepared.

Thereafter, Cu was adhered to one of the faces of each metal plate by avacuum deposition, the metal plate was stacked on the both faces of theceramics substrate so that the face of the metal plate on which theevaporation is performed faces the ceramics substrate, and thereby alayered body is formed.

The layered body was heated in a vacuum furnace (the degree of vacuum is10⁻³ Pa to 10⁻⁵ Pa) in a state where a pressure of 1 to 5 kgf/cm² wasapplied thereto in a stacked direction, and a power module substrateprovided with a ceramics substrate, a circuit layer, and a metal layerwas manufactured.

As described above, in the example 2, two kinds of power modulesubstrates were employed.

Here, adherence amounts of the adhered Cu (thickness of Cu) by vacuumdeposition were different from each other by five parameters (fivelevels), and were 0.1 μm, 0.5 μm, 1.0 μm, 2.0 μm, and 3.0 μm.

In addition, the heating temperatures were different from each other bythree parameters (three levels), and were 610° C., 630° C., and 650° C.

Consequently, a total of thirty kinds of power module substrates wereformed.

An aluminum plate (A6063) was connected to the metal layer of the powermodule substrate that were formed in this manner with a buffer layercomposed of 4N aluminum and having a thickness of 0.9 mm interposedtherebetween, the aluminum plate corresponding to a top panel of aheatsink, and having lengths of 50 mm and 60 mm and a thickness of 5 mm.

Consequently, a total of thirty kinds of test pieces were prepared.

Subsequently, before the thirty kinds of test pieces being subjected toa heat-load cycle test, the percentage of connected-surface area(junction rate) in the joint interface between the ceramics substrateand the metal plate was determined.

As a method for calculating the junction rate, the method forcalculating the junction rate by use of an ultrasonic imaging device(frequency of transducer is 15 MHz) was adopted as described in Example1.

In addition, the junction rate between a ceramics substrate and a metalplate was 100%, before a heat-load cycle test is performed.

Subsequently, a total of thirty kinds of test pieces were subjected toheat-load cycles of −40° C. to 105° C. by 3000 times under load, and thepresence or absence of cracks in the ceramics substrate was confirmed.

In addition, in this experiment, two sets of thirty kinds of test pieceswere prepared, and the presence or absence of cracks in the ceramicssubstrate was confirmed.

The results were shown in FIGS. 16A and 16B.

An evaluation result of the power module substrate that is obtained byevaporating and adhering Cu to the ceramics substrate is shown in FIG.16A.

In addition, an evaluation result of the power module substrate that isobtained by evaporating and adhering Cu to the metal plate is shown inFIG. 16B.

In addition, the power module substrate is represented by the symbol“◯”, in which cracks were not generated in the ceramics substrate inboth two test pieces, the power module substrate is presented by thesymbol “Δ”, in which cracks were generated in the ceramics substrate inone of two test pieces, and the power module substrate is represented bythe symbol “X”, in which cracks were generated in the ceramics substratein both two test pieces.

In addition, the junction rate of a total of thirty kinds of test pieceswas determined after the 3000 heat-load cycles described above wereperformed.

Specifically, by the same method as the above-described method in whichthe ultrasonic imaging device was used, the junction rate between aceramics substrate and a metal plate, that is, the junction rate afterthe 3000 heat-load cycles were performed, was determined.

As a result, evaluation results of the power module substrate wereobtained.

An evaluation result of the power module substrate that is obtained byevaporating and adhering Cu to the ceramics substrate is shown in FIG.17A.

In addition, an evaluation result of the power module substrate that isobtained by evaporating and adhering Cu to the metal plate is shown inFIG. 17B.

In addition, in FIGS. 17A and 17B, the power module substrate isrepresented by the symbol “◯”, in which the junction rate is 85% or moreafter the power module substrate is subjected to a 3000 cyclical thermalload; the power module substrate is represented by the symbol “Δ”, inwhich the junction rate is greater than or equal to 70% and less than85% after the power module substrate is subjected to a 3000 cyclicalthermal load; and the power module substrate is represented by thesymbol “X”, in which the junction rate is less than 70% after the powermodule substrate is subjected to a 3000 cyclical thermal load.

As shown in FIGS. 16A and 16B, it was confirmed that, as the thicknessof Cu formed in a Cu-adhering step increases, cracks in the ceramicssubstrate composed of AlN are easily generated.

In addition, in the test piece in which the thickness of Cu is 2 μm, itwas confirmed that, as the heating temperature increases, cracks in theceramics are suppressed more.

In addition, as shown in FIGS. 17A and 17B, it was confirmed that, asthe heating temperature increases, the junction reliability wasimproved.

In addition, in the case where the thickness of Cu is approximately 2μm, even if the heating temperature is low, it was confirmed that thejunction reliability was improved.

According to the test result, in the ceramics substrate composed of AlN,it is confirmed that the thickness of Cu existing at the boundary facebetween the metal plate and the ceramics substrate is preferably lessthan or equal to 2.5 μm at the time of connecting.

Example 3

In the example 3 described below, with reference to FIGS. 18A and 18B,and FIGS. 19A and 19B, the results of confirmatory experiments whichwere performed in order to confirm the effectivity of the power modulesubstrate of the third embodiment are described.

Firstly, as the power module substrate used for the experiment, a powermodule substrate was manufactured by the following method ofmanufacturing.

Specifically, a ceramics substrate composed of Si₃N₄ having 40 mm squareand a thickness of 0.32 mm, and two metal plates composed of aluminum 4Nhaving a thickness of 0.6 mm were prepared.

Thereafter, Cu was adhered to the both faces of the ceramics substrateby a vacuum deposition, and a layered body was formed by stacking themetal plates on both faces of the ceramics substrate.

The layered body was heated in a vacuum furnace (the degree of vacuum is10⁻³ Pa to 10⁻⁵ Pa) in a state where a pressure of 1 to 5 kgf/cm² wasapplied thereto in a stacked direction, and a power module substrateprovided with a ceramics substrate, a circuit layer, and a metal layerwas manufactured.

In a way similar to the above-described manner, a ceramics substratecomposed of Si₃N₄ having 40 mm of square and a thickness of 0.32 mm, andtwo metal plates composed of aluminum 4N having a thickness of 0.6 mmwere prepared.

Thereafter, Cu was adhered to one of the faces of each metal plate by avacuum deposition, the metal plate was stacked on the both faces of theceramics substrate so that the face of the metal plate on which theevaporation is performed faces the ceramics substrate, and thereby alayered body is formed.

The layered body was heated in a vacuum furnace (the degree of vacuum is10⁻³ Pa to 10⁻⁵ Pa) in a state where a pressure of 1 to 5 kgf/cm² wasapplied thereto in a stacked direction, and a power module substrateprovided with a ceramics substrate, a circuit layer, and a metal layerwas manufactured.

As described above, in the example 3, two kinds of power modulesubstrates were employed.

Here, adherence amounts of the adhered Cu (thickness of Cu) by vacuumdeposition were different from each other by five parameters (fivelevels), and were 0.1 μm, 0.5 μm, 1.0 μm, 2.0 μm, and 3.0 μm.

In addition, the heating temperatures were different from each other bythree parameters (three levels), and were 610° C., 630° C., and 650° C.

Consequently, a total of thirty kinds of power module substrates wereformed.

An aluminum plate (A6063) was connected to the metal layer of the powermodule substrate that were formed in this manner with a buffer layercomposed of 4N aluminum and having a thickness of 0.9 mm interposedtherebetween, the aluminum plate corresponding to a top panel of aheatsink, and having lengths of 50 mm and 60 mm and a thickness of 5 mm.

Consequently, a total of thirty kinds of test pieces were prepared.

Subsequently, before the thirty kinds of test pieces being subjected toa heat-load cycle test, the percentage of connected-surface area(junction rate) in the joint interface between the ceramics substrateand the metal plate was determined.

As a method for calculating the junction rate, the method forcalculating the junction rate by use of an ultrasonic imaging device(frequency of transducer is 15 MHz) was adopted as described in Example1.

In addition, the junction rate between a ceramics substrate and a metalplate was 100%, before a heat-load cycle test is performed.

Subsequently, a total of thirty kinds of test pieces were subjected toheat-load cycles of −40° C. to 105° C. by 3000 times under load, and thepresence or absence of cracks in the ceramics substrate was confirmed.

In addition, in this experiment, two sets of thirty kinds of test pieceswere prepared, and the presence or absence of cracks in the ceramicssubstrate was confirmed.

The results were shown in FIGS. 18A and 18B.

An evaluation result of the power module substrate that is obtained byevaporating and adhering Cu to the ceramics substrate is shown in FIG.18A.

In addition, an evaluation result of the power module substrate that isobtained by evaporating and adhering Cu to the metal plate is shown inFIG. 18B.

In addition, the power module substrate is represented by the symbol“◯”, in which cracks were not generated in the ceramics substrate inboth two test pieces, the power module substrate is presented by thesymbol “Δ”, in which cracks were generated in the ceramics substrate inone of two test pieces, and the power module substrate is represented bythe symbol “X”, in which cracks were generated in the ceramics substratein both two test pieces.

In addition, the junction rate of a total of thirty kinds of test pieceswas determined after the 3000 heat-load cycles described above wereperformed.

Specifically, by the same method as the above-described method in whichthe ultrasonic imaging device was used, the junction rate between aceramics substrate and a metal plate, that is, the junction rate afterthe 3000 heat-load cycles were performed, was determined.

As a result, evaluation results of the power module substrate wereobtained.

An evaluation result of the power module substrate that is obtained byevaporating and adhering Cu to the ceramics substrate is shown in FIG.19A.

In addition, an evaluation result of the power module substrate that isobtained by evaporating and adhering Cu to the metal plate is shown inFIG. 19B.

In addition, in FIGS. 19A and 19B, the power module substrate isrepresented by the symbol “◯”, in which the junction rate is 85% or moreafter the power module substrate is subjected to a 3000 cyclical thermalload; the power module substrate is represented by the symbol “Δ”, inwhich the junction rate is greater than or equal to 70% and less than85% after the power module substrate is subjected to a 3000 cyclicalthermal load; and the power module substrate is represented by thesymbol “X”, in which the junction rate is less than 70% after the powermodule substrate is subjected to a 3000 cyclical thermal load.

As shown in FIGS. 18A and 18B, in the ceramics substrate composed ofSi₃N₄, cracks in the ceramics substrate were not confirmed under thecondition of the present experiment.

In addition, as shown in FIGS. 19A and 19B, it was confirmed that, asthe heating temperature increases, the junction reliability wasimproved.

In addition, in the case where the thickness of Cu is approximately 2.0μm, even if the heating temperature is low, it was confirmed that thejunction reliability was improved.

According to the test result, in the ceramics substrate composed ofSi₃N₄, it is confirmed that the thickness of Cu existing at the boundaryface between the metal plate and the ceramics substrate is preferably0.15 μm to 3 μm at the time of connecting.

Example 4

In the example 4 described below, with reference to FIGS. 24A, 24B, 25A,and 25B, the results of confirmatory experiments which were performed inorder to confirm the effectivity of the power module substrate of thefourth embodiment are described.

Firstly, as the power module substrate used for the experiment, a powermodule substrate was manufactured by the following method ofmanufacturing.

Specifically, a ceramics substrate composed of Al₂O₃ having 40 mm squareand a thickness of 0.635 mm, and two metal plates composed of aluminum4N having a thickness of 0.6 mm were prepared.

Thereafter, Cu was adhered to the both faces of the ceramics substrateby a vacuum deposition, and a layered body was formed by stacking themetal plates on both faces of the ceramics substrate.

The layered body was heated in a vacuum furnace (the degree of vacuum is10⁻³ Pa to 10⁻⁵ Pa) in a state where a pressure of 1 to 5 kgf/cm² wasapplied thereto in a stacked direction, and a power module substrateprovided with a ceramics substrate, a circuit layer, and a metal layerwas manufactured.

In a way similar to the above-described manner, a ceramics substratecomposed of Al₂O₃ having 40 mm of square and a thickness of 0.635 mm,and two metal plates composed of aluminum 4N having a thickness of 0.6mm were prepared.

Thereafter, Cu was adhered to one of the faces of each metal plate by avacuum deposition, the metal plate was stacked on the both faces of theceramics substrate so that the face of the metal plate on which theevaporation is performed faces the ceramics substrate, and thereby alayered body is formed.

The layered body was heated in a vacuum furnace (the degree of vacuum is10⁻³ Pa to 10⁻⁵ Pa) in a state where a pressure of 1 to 5 kgf/cm² wasapplied thereto in a stacked direction, and a power module substrateprovided with a ceramics substrate, a circuit layer, and a metal layerwas manufactured.

As described above, in the example 4, two kinds of power modulesubstrates were employed.

Here, adherence amounts of the adhered Cu (thickness of Cu) by vacuumdeposition were different from each other by five parameters (fivelevels), and were 0.1 μm, 0.5 μm, 1.0 μm, 2.0 μm, and 3.0 μm.

In addition, the heating temperatures were different from each other bythree parameters (three levels), and were 610° C., 630° C., and 650° C.

Consequently, a total of thirty kinds of power module substrates wereformed.

An aluminum plate (A6063) was connected to the metal layer of the powermodule substrate that were formed in this manner with a buffer layercomposed of 4N aluminum and having a thickness of 0.9 mm interposedtherebetween, the aluminum plate corresponding to a top panel of aheatsink, and having lengths of 50 mm and 60 mm and a thickness of 5 mm.

Consequently, a total of thirty kinds of test pieces were prepared.

Subsequently, before the thirty kinds of test pieces being subjected toa heat-load cycle test, the percentage of connected-surface area(junction rate) in the joint interface between the ceramics substrateand the metal plate was determined.

As a method for calculating the junction rate, the method forcalculating the junction rate by use of an ultrasonic imaging device(frequency of transducer is 15 MHz) was adopted as described in Example1.

In addition, the junction rate between a ceramics substrate and a metalplate was 100%, before a heat-load cycle test is performed.

Subsequently, a total of thirty kinds of test pieces were subjected toheat-load cycles of −40° C. to 105° C. by 3000 times under load, and thepresence or absence of cracks in the ceramics substrate was confirmed.

In addition, in this experiment, two sets of thirty kinds of test pieceswere prepared, and the presence or absence of cracks in the ceramicssubstrate was confirmed.

An evaluation result of the power module substrate that is obtained byevaporating and adhering Cu to the ceramics substrate is shown in FIG.24A.

In addition, an evaluation result of the power module substrate that isobtained by evaporating and adhering Cu to the metal plate is shown inFIG. 24B.

In addition, the power module substrate is represented by the symbol“◯”, in which cracks were not generated in the ceramics substrate inboth two test pieces, the power module substrate is presented by thesymbol “Δ”, in which cracks were generated in the ceramics substrate inone of two test pieces, and the power module substrate is represented bythe symbol “X”, in which cracks were generated in the ceramics substratein both two test pieces.

In addition, the junction rate of a total of thirty kinds of test pieceswas determined after the 3000 heat-load cycles described above wereperformed.

Specifically, by the same method as the above-described method in whichthe ultrasonic imaging device was used, the junction rate between aceramics substrate and a metal plate, that is, the junction rate afterthe 3000 heat-load cycles were performed, was determined.

As a result, evaluation results of the power module substrate wereobtained.

An evaluation result of the power module substrate that is obtained byevaporating and adhering Cu to the ceramics substrate is shown in FIG.25A.

In addition, an evaluation result of the power module substrate that isobtained by evaporating and adhering Cu to the metal plate is shown inFIG. 25B.

In addition, in FIG. 25B, the power module substrate is represented bythe symbol “◯”, in which the junction rate is 85% or more after thepower module substrate is subjected to a 3000 cyclical thermal load; thepower module substrate is represented by the symbol “Δ”, in which thejunction rate is greater than or equal to 70% and less than 85% afterthe power module substrate is subjected to a 3000 cyclical thermal load;and the power module substrate is represented by the symbol “X”, inwhich the junction rate is less than 70% after the power modulesubstrate is subjected to a 3000 cyclical thermal load.

As shown in FIGS. 25A and 25B, it was confirmed that, as the thicknessof Cu formed in a Cu-adhering step increases, cracks in the ceramicssubstrate composed of Al₂O₃ are easily generated.

In addition, in the test piece in which the thickness of Cu is 2 μm, itwas confirmed that, as the heating temperature increases, cracks in theceramics are suppressed more.

In addition, as shown in FIGS. 25A and 25B, it was confirmed that, asthe heating temperature increases, the junction reliability wasimproved.

In addition, in the case where the thickness of Cu is approximately 1μm, even if the heating temperature is low, it was confirmed that thejunction reliability was improved.

According to the test result, in the ceramics substrate composed ofAl₂O₃, it is confirmed that the thickness of Cu existing at the boundaryface between the metal plate and the ceramics substrate is preferablyless than or equal to 2.5 μm at the time of connecting.

Example 5

In the examples 5 and 6 described below, with reference to FIG. 34 andTable 1, the results of confirmatory experiments which were performed inorder to confirm the effectivity of the power module substrate of thefifth and sixth embodiments are described.

As shown in FIG. 34, confirmatory experiment was performed by use of apower module substrate having: a ceramics substrate 211 composed of AlNhaving a thickness of 0.635 mm; a circuit layer 212 composed of 4Naluminum having a thickness of 0.6 mm; a metal layer 213 composed of 4Naluminum having a thickness of 0.6 mm; a top panel section 5 composed ofan aluminum alloy (A6063) having a thickness of 5 mm; and a buffer layer15 composed of 4N aluminum having a thickness of 1.0 mm, as common powermodule substrates in the comparative example and example 5.

In example 5, metal plates that become the circuit layer 212 and themetal layer 213 were connected to the ceramics substrate 211 by use ofan Al—Si system brazing filler metal, after Cu was adhered to thesurface of the ceramics substrate 211 by a sputtering.

In contrast, in the comparative example, Cu was not introduced into thejoint interfaces between the ceramics substrate 211 and the metalplates, and the metal plates that become the circuit layer 212 and themetal layer 213 were connected to the ceramics substrate 211 by use ofan Al—Si system brazing filler metal.

Consequently, a test piece of example 5 and a test piece of thecomparative example were prepared.

Subsequently, before the test pieces being subjected to a heat-loadcycle test, the percentage of connected-surface area (junction rate) inthe joint interface between the ceramics substrate and the metal platewas determined.

As a method for calculating the junction rate, the method forcalculating the junction rate by use of an ultrasonic imaging device(frequency of transducer is 15 MHz) was adopted as described in Example1.

In addition, before a heat-load cycle test is performed, the junctionrate between a ceramics substrate and a metal plate of the test piece ofexample 5 was 100%, and the junction rate between a ceramics substrateand a metal plate of the test piece of the comparative example was99.8%.

Next, evaluation of the junction reliability by use of the test pieceswas performed.

In the evaluation of the junction reliability, regarding the junctionrate at which after heat-load cycles (−45° C. to 125° C.) wererepeatedly performed, the comparative example was compared to example 5.

Specifically, by the same method as the above-described method in whichthe ultrasonic imaging device was used, junction rate between theceramics substrate and the metal plate in the comparative example andexample 5 was determined.

Furthermore, the junction rates were determined after each of heat-loadcycles of 1000 times, 2000 times, and 3000 times is performed.

Consequently, the evaluation result of the power module substrate wasobtained.

The evaluation result was shown in Table 1.

TABLE 1 INTRODUCING OF JUNCTION RATE AFTER BEING SUBJECTED Cu INTO JOINTTO HEAT-LOAD CYCLE INTERFACE 1000 TIMES 2000 TIMES 3000 TIMES EXAMPLE 5PRESENCE  100%  100% 99.2% COMPARATIVE ABSENCE 99.8% 94.2% 91.5% EXAMPLE

In the comparative example, in which connection is performed by use ofan Al—Si system brazing filler metal without introducing Cu into thejoint interface, the junction rate was near 100% (99.8%) after 1000heat-load cycles.

However, it was confirmed that the junction rate decreases after 2000heat-load cycles (94.2%), and the junction rate decreased to 91.5% afterthe 3000 heat-load cycles.

On the other hand, in example 5, in which Cu was introduced into thejoint interface, even if the heat-load cycles were performed 2000 times,the junction rate did not decrease.

The junction rate was 99.2% after the 3000 heat-load cycles.

According to the confirmatory experiment, it was confirmed that theheat-load cycle reliability is improved by introducing Cu into the jointinterface.

Example 6

Subsequently, assay result of component of the metal layer in the powermodule substrates of the fifth and sixth embodiments is described.

The circuit layer 212 composed of 4N aluminum having a thickness of 0.6mm and the metal layer 213 composed of 4N aluminum having a thickness of0.6 mm were connected to the ceramics substrate 211 composed of AlNhaving a thickness of 0.635 mm, and the power module substrate wasmanufactured.

Here, in examples 6A to 6C, a Cu-layer having a thickness of 1.5 μm wasformed on the surface of a brazing filler metal having Si includingAl-7.5 wt %, and the circuit layer 212 and the metal layer 213 wereconnected to the ceramics substrate 211 by use of the brazing fillermetal having Si including Al-7.5 wt %.

In addition, the connection temperatures were different from each otherby three parameters (3 levels), and were 610° C., 630° C., and 650° C.

Here, in examples 6D to 6F, a Cu-layer having a thickness of 1.5 μm wasformed on the surface of the ceramics substrate 211, and the circuitlayer 212 and the metal layer 213 were connected to the ceramicssubstrate 211 by use of a brazing filler metal having Si includingAl-7.5 wt %.

In addition, the connection temperatures were different from each otherby three parameters (3 levels), and were 610° C., 630° C., and 650° C.

Regarding the examples 6A to 6F, quantitative analysis was performed forthe Cu concentration and the Si concentration by use of EPMA, at acenter portion in a width direction of the boundary face between themetal layer and the ceramics substrate, and at the end portion in thewidth direction of the boundary face.

The result was shown in Table 2.

TABLE 2 Si (wt %) Cu (wt %) CONNECTION CENTER END CENTER END TEMPERATURE(° C.) PORTION PORTION PORTION PORTION EXAMPLE 6A 610 0.084 1.091 0.4810.943 EXAMPLE 6B 630 0.113 1.455 0.457 0.854 EXAMPLE 6C 650 0.106 1.2430.418 0.933 EXAMPLE 6D 610 0.102 1.314 0.634 1.066 EXAMPLE 6E 630 0.1081.257 0.370 1.043 EXAMPLE 6F 650 0.087 1.066 0.355 1.320

According to the result of quantitative analysis, in the case where theCu-layer was formed and the ceramics substrate was connected to themetal plate by use of an Al—Si system brazing filler metal, it wasconfirmed that the Si concentration of the portion which is close to thejoint interface is 0.05 to 0.5 wt % and the Cu concentration thereof wasin the range of 0.05 to 1.0 wt % at the center portion of the widthdirection.

In addition, it is confirmed that Si and Cu exist at the end portion inthe width direction with a high level of concentration.

1-9. (canceled)
 10. A power module substrate comprising: a ceramicssubstrate composed of AlN or Si₃N₄, having a surface; a metal plateconnected to the surface of the ceramics substrate, composed of purealuminum; and a high-Cu concentration section formed at a jointinterface between the metal plate and the ceramics substrate, having aCu concentration that is more than twice the Cu concentration in themetal plate.
 11. The power module substrate according to claim 10,wherein an oxygen concentration in the high-Cu concentration section isgreater than oxygen concentrations in the metal plate and the ceramicssubstrate.
 12. The power module substrate according to claim 10, whereinthe ceramics substrate is composed of AlN; and a mass ratio of Al, Cu,O, and N is Al:Cu:O:N=50 to 90 wt %:1 to 10 wt %:2 to 20 wt %:25 wt % orless when the joint interface including the high-Cu concentrationsection is analyzed by an energy dispersive X-ray spectroscopy.
 13. Thepower module substrate according to claim 10, wherein the ceramicssubstrate is composed of Si₃N₄; and a mass ratio of Al, Si, Cu, O, and Nis Al:Si:Cu:O:N=15 to 45 wt %:15 to 45 wt %:1 to 10 wt %:2 to 20 wt %:25wt % or less when the joint interface including the high-Cuconcentration section is analyzed by an energy dispersive X-rayspectroscopy.
 14. A power module comprising: a power module substrateaccording to claim 10; and an electronic component mounted on the powermodule substrate.
 15. A method for manufacturing a power modulesubstrate, comprising: preparing a ceramics substrate composed of AlN, ametal plate composed of pure aluminum, and a Cu-layer having a thicknessof 0.15 μm to 3 μm; stacking the ceramics substrate and the metal platein layers with the Cu-layer interposed therebetween; pressing theceramics substrate, the Cu-layer, and the metal plate which were stackedin layers in a stacked direction, and heating the ceramics substrate,the Cu-layer, and the metal plate; forming a fusion aluminum layer at aboundary face between the ceramics substrate and the metal plate;solidifying the fusion aluminum layer by cooling the fusion aluminumlayer; and forming a high-Cu concentration section at a joint interfacebetween the ceramics substrate and the metal plate, the high-Cuconcentration section having a Cu concentration that is more than twicethe Cu concentration in the metal plate.
 16. The method formanufacturing a power module substrate according to claim 15, whereinwhen stacking the ceramics substrate and the metal plate in layers withthe Cu-layer interposed therebetween, the Cu-layer is disposed byinserting a copper foil between the ceramics substrate and the metalplate.
 17. The method for manufacturing a power module substrateaccording to claim 15, wherein the Cu-layer is adhered to at least oneof the ceramics substrate and the metal plate before stacking theceramics substrate, the Cu-layer, and the metal plate in layers.
 18. Themethod for manufacturing a power module substrate according to claim 17,wherein when the Cu is adhered to at least one of the ceramics substrateand the metal plate, Cu is adhered to at least one of the ceramicssubstrate and the metal plate, by a method selected from the groupconsisting of an evaporation method, a sputtering method, a platingmethod, and a method of applying a Cu-paste.
 19. A method formanufacturing a power module substrate, comprising: preparing a ceramicssubstrate composed of Si₃N₄, a metal plate composed of pure aluminum,and a Cu-layer having a thickness of 0.15 μm to 3 μm; stacking theceramics substrate and the metal plate in layers with the Cu-layerinterposed therebetween; pressing the ceramics substrate, the Cu-layer,and the metal plate which were stacked in layers in a stacked direction,and heating the ceramics substrate, the Cu-layer, and the metal plate;forming a fusion aluminum layer at a boundary face between the ceramicssubstrate and the metal plate; solidifying the fusion aluminum layer bycooling the fusion aluminum layer; and forming a high-Cu concentrationsection at a joint interface between the ceramics substrate and themetal plate, the high-Cu concentration section having a Cu concentrationthat is more than twice the Cu concentration in the metal plate.
 20. Themethod for manufacturing a power module substrate according to claim 19,wherein when stacking the ceramics substrate and the metal plate inlayers with the Cu-layer interposed therebetween, the Cu-layer isdisposed by inserting a copper foil between the ceramics substrate andthe metal plate.
 21. The method for manufacturing a power modulesubstrate according to claim 19, wherein the Cu-layer is adhered to atleast one of the ceramics substrate and the metal plate before stackingthe ceramics substrate, the Cu-layer, and the metal plate in layers. 22.The method for manufacturing a power module substrate according to claim21, wherein when the Cu is adhered to at least one of the ceramicssubstrate and the metal plate, Cu is adhered to at least one of theceramics substrate and the metal plate, by a method selected from thegroup consisting of an evaporation method, a sputtering method, aplating method, and a method of applying a Cu-paste.
 23. A power modulesubstrate comprising: a ceramics substrate composed of Al₂O₃, having asurface; a metal plate connected to the surface of the ceramicssubstrate, composed of pure aluminum; and a high-Cu concentrationsection formed at a joint interface between the metal plate and theceramics substrate, having a Cu concentration that is more than twicethe Cu concentration in the metal plate.
 24. The power module substrateaccording to claim 23, wherein a mass ratio of Al, Cu, and O isAl:Cu:O=50 to 90 wt %:1 to 10 wt %:0 to 45 wt % when the joint interfaceincluding the high-Cu concentration section is analyzed by an energydispersive X-ray spectroscopy.
 25. A power module comprising: a powermodule substrate according to claim 23; and an electronic componentmounted on the power module substrate.
 26. A method for manufacturing apower module substrate, comprising: preparing a ceramics substratecomposed of Al₂O₃, a metal plate composed of pure aluminum, and aCu-layer having a thickness of 0.15 μm to 3 μm; stacking the ceramicssubstrate and the metal plate in layers with the Cu-layer interposedtherebetween; pressing the ceramics substrate, the Cu-layer, and themetal plate which were stacked in layers in a stacked direction, andheating the ceramics substrate, the Cu-layer, and the metal plate;forming a fusion aluminum layer at a boundary face between the ceramicssubstrate and the metal plate; solidifying the fusion aluminum layer bycooling the fusion aluminum layer; and forming a high-Cu concentrationsection at a joint interface between the ceramics substrate and themetal plate, the high-Cu concentration section having a Cu concentrationthat is more than twice the Cu concentration in the metal plate.
 27. Themethod for manufacturing a power module substrate according to claim 26,wherein when stacking the ceramics substrate and the metal plate inlayers with the Cu-layer interposed therebetween, the Cu-layer isdisposed by inserting a copper foil between the ceramics substrate andthe metal plate.
 28. The method for manufacturing a power modulesubstrate according to claim 26, wherein the Cu-layer is adhered to atleast one of the ceramics substrate and the metal plate before stackingthe ceramics substrate, the Cu-layer, and the metal plate in layers. 29.The method for manufacturing a power module substrate according to claim28, wherein when the Cu is adhered to at least one of the ceramicssubstrate and the metal plate, Cu is adhered to at least one of theceramics substrate and the metal plate, by a method selected from thegroup consisting of an evaporation method, a sputtering method, aplating method, and a method of applying a Cu-paste. 30-37. (canceled)